HOW  TO  SEE 

WITH 

THE  MICROSCOPE: 

BEING 
USEFUL  HINTS  CONNECTED  WITH  THE    SELECTION    AND    USE 

OF  THE  INSTRUMENT;  ALSO  SOME  DISCUSSION  OF  THE 

CLAIMS    AND    CAPACITY    OF    THE     MODERN     HIGH- 
ANGLED     OBJECTIVES,    AS     COMPARED    WITH 
THOSE    OF    MEDIUM  APERTURE;    WITH 
INSTRUCTIONS  AS  TO  THE  SELEC- 
TION AND    USE    OF    AMERI- 
CAN OBJECT-GLASSES 
OF    WIDE    APER- 
TURES. 

ar 

J.  EDWARDS   SMITH,   M.  D., 

PROFESSOR  OF  PJSTOLOUY  AND  MICROSCOPY  IN  THE  CLEVELAND  (O.),  HOM- 
EOPATHIC HOSPITAL  COLLEGE;  CORRESPONDING  MEMBER  OF  THE  SAX 
FRANCISCO,  THE  DUNKIRK,  AND  ILLINOIS.  STATE  MICROSCOPICAL 
SOCIETIES;  MEMBER  OF  THE  AMERICAN  ASSOCIATION 
FOR  THE  ADVANCEMENT  OF  SCIENCE,  ETC. 


ILLUSTRATED. 


CHICAGO  : 
DUNCAN  BROTHERS. 

1880. 


Copyrighted  by 

DUNCAN  BROTHERS, 

131  and  133  South  Clark  street, 

CHICAGO. 


r 


DEDICATION: 

TO 
THE  HON.  P.  H.  WATSON, 

WHOSE    FRIENDSHIP    HAS   ENCOURAGED   AND    WHOSE    PARTICIPATION    HAS 
GIVEN    DOUBLE    PLEASURE  TO  THE  INVESTIGATIONS  RECORDED 
IN    THESE  PAGES  ?  THE  TRUE  FRIEND,   AND  THE  LIB- 
ERAL PATRON  OF  SCIENTIFIC  EXPERI- 
MENT, THIg  LITTLE  BOOK 
IS  DEDICATED 
BY  THE 

AUTHOR. 


PREFACE. 


INTRODUCTORY   AND   APOLOGETICAL. 

In  the  spring  of  1874  I  received  from  K.  B.  Tolles, 
Esq.,  (the  well-known  optician  of  Boston,  Mass.,)  a 
one-sixth  immersion  object  glass,  which  he  requested 
me  to  study  carefully,  and  to  report  the  results  to  him. 

The  angular  aperture  of  this  new  one-sixth  was  said 
to  be  180°,  and  the  objective  was  one  of  the  tirst  "  du- 
plex "  or  four-system  glasses  devised  by  Mr.  Tolles,  and 
destined,  in  a  few  short  months,  to  create  quite  a  stir  in 
microscope  circles. 

Having,  at  that  date,  leisure  at  my  command,  and 
being  very  much  interested  in  the  performance  of  ob- 
ject glasses,  I  was  very  glad  to  give  this  objective  careful 
and  prolonged  attention.  The  result  was,  that  after 
thirty  days'  experience  I  had  arrived  at  a  settled  con- 
viction that  Mr.  Tolles  had  made  a  decided  advance  in 
the  construction  and  performance  of  microscope  object 
glasses. 

Believing  this  experience  of  mine  to  be  of  value  to 
microscopists,  I  wrote  a  short  account  of  the  perform- 
ance of  this  one-sixth,  which  was  published  in  the  Cin- 
cinnati Medical  News. 

Shortly  afterwards  Mr.  Tolles  kindly  sent  me  another 
of  the  "  duplex  "  or  four-system  objectives,  this  time  a 


10  PREFACE. 

one-tenth.  This  glass  also  occupied  my  leisure  time  for 
a  considerable  interval. 

The  performance  of  the  one-tenth  fully  sustained  the 
high  appreciation  I  had  formed  of  the  performance  of 
the  duplex  glasses.  In  some  respects  the  work  of  the 
one- tenth  excelled  that  of  the  one-sixth. 

The  article  published  in  the  Cincinnati  Medical  News 
was  therefore  supplemented  by  several  other  communi- 
cations written  by  me,  giving  my  further  experience 
with  the  duplex  objectives. 

Among  the  conclusions  I  had  arrived  at  from  the  study 
of  the  new  four-system  glasses  were  to  be  found  em- 
bodied ideas  radically  opposed  to  popular  dogmas  which 
were  at  that  date  fully  received  and  accepted  by  micro- 
scopists  generally  as  settled  matters  of  fact.  For  in- 
stance, it  was  claimed  for  the  duplex  one-sixth  and  one- 
tenth  that  either  of  these  objectives  would  not  only  do 
the  work  of,  but  excel  the  performance  (under  amplifi- 
cations from  275  to  4,000  diameters)  of  any  one-fiftieth 
extant.  Furthermore,  it  was  claimed  that  the  central 
light  work  of  the  new  wide  apertured  duplex  objectives 
would  surpass  that  of  the  low  angles. 

Referring  to  the  resolution  of  the  severest  test  objects, 
it  was  the  express  purpose  of  the  said  contributions  to 
the  Cincinnati  Medical  News  to  claim  and  insist  on,  as 
a  stubborn  fact,  that  the  work  of  the  duplex  one-sixth 
or  one-tenth  excelled  that  of  any  glass  extant,  "  be  it  a 
one-fifth  or  a  one-fiftieth." 

These,  as  well  as  other  statements  so  thoroughly  hete- 
rodox to  established  belief,  met,  as  a  matter  of  course, 


PREFACE.  11 

with  earnest  opposition  from  my  readers.  A  large  cor- 
respondence ensued,  while  many  microscopists  visited 
me  for  the  purpose  of  witnessing,  by  way  of  ocular 
demonstrations,  the  performance  of  the  duplex  glasses. 

Meanwhile,  in  London,  England,  a  lively  controversy, 
known  in  microscope  circles  as  "  the  war  of  the  aper- 
tures," appeared  in  the  columns  of  the  London  Monti tly 
Journal  of  Microscopy,  in  which  controversy  the  posi- 
tions assumed  by  Mr.  Tolles  were  assailed  by  Mr.  F.  A. 
Wenham.  The  issues  involved,  however,  appertained 
only  to  optical  possibilities,  the  performance  of  the  du- 
plex objectives  being  an  entirely  outside  matter.  During 
the  London  battle  Mr.  Tolles  was  ably  assisted  by  Dr. 
J.  J.  Woodward,  of  Washington,  D.  C.,  and  by  Piof. 
Keith  of  Georgetown.  Suffice  it  here  to  say,  that  froir 
the  standpoint  of  optical  science  Mr.  Tolles  maintains 
his  positions,  a  fact,  I  believe,  now  generally  admittedt 

And  now,  after  a  period  of  nearly  six  years,  it  is  to 
me  a  matter  of  pride  to  here  record  that  of  the  several 
4 '  heterodox  "  positions  I  had  assumed  in  public  print, 
there  has  occurred,  neither  in  the  interim,  or  at  this 
present  writing,  no  occasion  to  retract  one  word  of  what 
was  claimed  by  me  in  my  former  contributions  to  the 
Cincinnati  Medical  News.  The  duplex  objectives  have 
steadily,  and  perforce  of  intrinsic  worth,  forced  their 
way  into  general  use,  while  the  leading  opticians  are 
exerting  themselves  to  still  further  improve  their 
performance. 

Having,  as  I  have  above  briefly  set  forth,  had  a  very 
large  experience  with  the  four-system  objectives,  it  was 


12  PREFACE. 

suggested  to  the  author  that  a  small  work,  giving  in 
detail  the  manipulations  of  the  new  objectives,  with, 
perhaps,  some  other  items  resulting  from  an  experience 
of  over  fifteen  years  as  a  microscopist,  would  not  only 
be  acceptable,  but  would  fill  a  place  at  present  unoccu- 
pied; and  it  is  in  response  to  this  suggestion  this  little 
book  is  presented,  with  the  hope  that  it  may  prove  of 
some  service  to  some  of  my  brother  microscopists. 

The  book  is  entirely  innocent  of  literary  pretensions. 
It  has  been  my  aim  to  express  myself  in  the  simplest 
possible  manner.  The  diction  is  at  times  redundant, 
gossipy  and  commonplace,  the  dominant  idea  through- 
out being  to  hold  a  good  natured  chat  with  my  readers* 

During  the  past  eight  years  the  author  has  received 
thousands  of  letters  asking  for  information  in  the  mat- 
ter of  microscope  object  glasses,  and  especially  has  his 
experience  been  called  on  as  to  methods  of  manipulation 
involved  in  the  use  of  wide  apertured  objectives.  In 
the  following  pages  he  has  endeavored  to  supply  this  in- 
formation, introducing,  it  is  believed,  the  first  attempt 
to  teach  the  difficult  art  of  collar  adjustment,  as  will  be 
seen  in  the  graduated  series  of  lessons,  which,  imperfect 
as  they  are,  it  is  hoped  will  nevertheless  be  of  value  to 
those  commencing  to  use  the  four-system  objectives. 

A.nd  now,  by  way  of  apology,  it  remains  to  state  that 
circumstances  entirely  unlocked  for,  and  entirely  beyond 
the  author's  control,  have  caused  a  delay  in  the  publica- 
tion, and  many  have  suffered  disappointment  therefrom. 
This  delay,  however,  has  furnished  me  with  the  oppor- 
tunity to  revise  the  MS.,  rendering  it,  I  trust,  more 


PREFACE.  13 

acceptable.  It  has  also  given  me  the  opportunity  to 
introduce  new  matter  not  originally  contemplated. 

During  the  period  of  delay  above  mentioned  the  writer 
was  in  receipt  of  hundreds  of  letters  of  enquiry  from 
as  many  kind  friends.  It  was  impossible  to  reply  to  all 
of  these.  He,  however,  improves  the  present  as  a  fit- 
ting occasion  to  return  his  grateful  thanks  to  those  of 
his  correspondents  for  the  tangible  evidences  of  confi- 
dence and  esteem  thus  manifested. 

And  to  the  Messrs.  Duncan  Bros.,  too,  is  he  under 
obligations  for  the  hearty  manner  in  which  they  took 
the  little  brochure  under  their  wing,  pushing  the  same 
through  the  press  with  their  accustomed  energy. 

323  Euclid  Avenue,  Cleveland,  O.,  September  1880. 


ACME   STAND. 


CONTENTS. 


PAGE. 

Introduction  and  Apologetical       .....  5 


CHAPTER  I. 

Something  about  American  Stands,  etc.  .  IT 

Zentmayer's  American  Centennial  Stands.          ...  34 

The  American  Histological  Stand 39 

Tolles'  large  "•  B  B  "  Microscope 47 

Tolles'  Largest  "  A  "  Microscope 48 

Tolles'  Student's  Microscope 49 

The  Professional  Microscope 53 

Large  Student's  Microscope           46 

Family  Microscope 57 

Bulloch's  First-Class  Microscope 59 

Small  best  Stand  "  A  B  "     .               67 

Mr.  Bulloch's "  D "  Stand       .        .        .        .        .       .       .  67 

Mr.  Bulloch's  New  Biological  Stand         ....  68 

R.  &.  J.  Beck's  Microscope     . 71 

Beck's  Popular  Microscope,  Minocular  or  Binocular     .  72 

Beck's  Economic  Microscope 72 

Beck's  New  Histological  Dissecting  Microscope     .       .  79 

The  New  National  Microscope 80 

The  New  Acme  Stand 84 

13 


14  CONTENTS. 


CHAPTEE  II. 

What  is  Augnlar  Aperture 93 

Angular  Aperture           ...              ....  93 

How  Shall  we  Measure  Angular  Aperture          ...  95 

Object  Glasses        .       , 97 

Something  Further  about  Objectives           ....  108 

Balsam  Apertures 123 

Flatness  of  Field              , 126 

Mounting  of  Objectives 129 

Nomenclature  of  Objectives 130 

Table  of  the  Magnifying  Power  of  Single  Convex  Lenses  134 


CHAPTER  III. 

Objectives  Continued           137 

Objectives  of  Lower  Balsam  Angle 144 

Adjustable  Objectives          ........  148 

Eye-Pieces .  156 


CHAPTER  IV. 

Manipulations  —  Wenham's  Reflex  Illuminator      .       .  157 

The  Woodward  Illuminator  ......  163 

Tolles'  Traverse  Lens  179 


CONTENTS.  •  15 


CHAPTER  V. 

Illumination .       .  .183 

Sunlight           ..........  186 

Artificial  Light 187 


CHAPTER  VI. 

Choice  of  Objectives  for  Regular  Work          ...  202 

Selection  of  Covering  Glass  213 

Bull's  Eye  Condenser  225 

Working  with  Low  Powers 225 

The  Spencer  one-inch  of  50°  —  Broad  Guage  Objectives, 

.etc.  230 


CHAPTER  VII. 

Work  with  the  Higher "  Powers "         .       .       .       .  .     235 

Position  of  Observer 246 

Mean  of  ten  Measurement  of  Moller  Test  Plates       .  .      253 

Position  of  Observer            '289 

Work  over  dry  Mounts  with  high  Aperture  Objectives  .      298 

Oil  Immersion  Object  Glasses     ....••  309 

Oil  Immersion  Objectives 310 


16  CONTENTS. 


CHAPTEE  VIII. 

A  Word  or  two  on  Volumetric  Analysis          .       .       .         318 

Apparatus  necessary 320 

Analysis  of  Urea,  etc 325 

Analysis  of  Sugar,  etc 332 

Preparation  of  Urinary  Constituents 339 

APPENDIX. 

Names  and  Address  of  Dealers  in  Microscopes,  Object- 
ives, etc.,  Alphabetically  Arranged    ....         341 

The  Investigator  Microscope 345 

International  Microscope  Stand, 348 

Prices  of  Accessories 352 

SUPPLEMENT. 

Contributions  to  the  Cincinnati  Medical  News        .       .  358 

High  Angles        .                                359 

Angular  Aperture  and  Central  Illumination       .        .        .  361 

On  the  Performance  of  Objections 368 

Angular  Aperture  once  More 370 

The  use  and  abuse  of  the  Microscope       ....  375 

A  Chapter  on  Elementary  Physics                 ,  393 

Choice  of  Objectives     .,,.....  397 
Microscopical  Examinations  of  Oleomargarine    .        .       .400 


HOW  TO  SEE  WITH  THE  MICROSCOPE. 


CHAPTER  I. 

SOMETHING   ABOUT   AMERICAN   STANDS,    ETC. 

The  choice  of  a  stand  is  a  matter  of  interest  to  every 
working  microscopist,  and  to  most  of  us  it  has  been  a 
source  of  much  annoyance  and  needless  expense.  It 
may  be  safely  affirmed  that  most  workers  have  wasted 
more  money  in  previous  purchases  of  unsatisfactory 
stands  than  would  suffice  to  pay  for  the  one  at  present 
in  use ;  very  many  indeed  would  feel  grateful  to  be  let 
off  with  this  record.  I  therefore  propose  to  assist  the 
novice  in  the  important  matter  of  the  selection  of  a 
stand,  and  shall,  with  this  end  purely  in  view,  give  him 
fearlessly  what,  in  my  opinion,  will  be  sound  advice. 

And  be  it  known  again  that  there  will  be  some  adver- 
tising done  in  this  department.  As  I  have  before  inti- 
mated, it  is  quite  impossible  to  say  what  I  shall  have  to 
say,  of  real  value  to  the  reader,  without  giving  promi- 
nence to  one  or  more  of  the  several  makers.  The  re- 
sponsibility is  mine,  and  I  accept  it.  It  has  been  my 
province,  in  times  past,  to  select  many  stands  for  my 
friends  and  acquaintances ;  those  who  have  visited  me 
with  the  special  object  to  ascertain  my  methods  of  using 
and  working  objectives  have,  in  many  instances,  fol- 


18  HOW   TO    SEE    WITH   THE    MICROSCOPE. 

lowed  my  recommendations  as  to  stands,  and  in  every 
•case,  I  believe,  have  expressed  to  me  their  satisfaction. 
The  author  has  not  in  the  past  stood  so  much  alone  as 
•to  his  ideas  of  a  stand  as  was  the  case  with  his  opinion 
*of  objectives. 

Now,  in  what  follows,  it  is  to  be  assumed  that  the 
reader  desires  one  stand,  and  one  only,  and  that  he 
wishes  to  invest  his  money  to  the  best  advantage,  i.  e., 
make  the  same  go  as  far  as  possible ;  that  he  desires  a 
really  good  and  reliable  instrument,  and  one  that  will 
last  for  a  lifetime. 

During  the  past  three  or  four  years,  the  microscope 
stand  has  been  greatly  improved,  both  in  Europe  and 
America,  and  as  a  rule,  really  serviceable  instruments 
*can  now  be  obtained  either  of  American  or  London 
-workmanship,  and  at  a  moderate  cost.  It  is  to  be  re- 
:gretted  that  our  German  friends  have  not  followed  suit, 
•but,  on  the  contrary,  have  been  content  with  the  old 
form  of  stands  which  were  patent  ten  years  ago. 

In  the  late  improvements  by  the  American  and  Lon- 
don makers,  it  is  first  noticealle  that  the  weight  of  the 
stand  has  been  considerably  reduced ;  the  old  idea,  that 
to  secure  sufficient  solidity  it  was  necessary  to  employ 
stands  weighing  from  twenty  to  forty  pounds,  being 
now  practically  abandoned. 

Again,  it  was  formerly  considered  a  sine  qua  non  that 
the  microscope  stage  be  thick  enough,  heavy  enough, 
and  solid  enough  to  bear  the  whacks  from  a  sledge- 
hammer. 

It  must  be  here  kept  in  mird  that  years  ago  there 


SOMETHING   ABOUT    AMERICAN   STANDS,    ETC.  19 

were  no  such  things  as  wide-angled  objectives,  and,  as 
a  matter  of  course,  the  work  was  principally  done 
with  central  or  centrally  disposed  light.  To  this  the 
old  and  heavy  stage  offered  no  objection,  for  it  was 
quite  possible,  with  the  aid  of  achromatic  condensers, 
prisms,  etc.,  to  work  with  all  the  obliquity  the  objective 
would  respond  to,  using  a  stage  two  or  three  inches  in 
thickness.  Luckily,  there  were  those  who  would  at 
times  "fight  objectives,"  play  with  diatoms,  etc.,  and 
in  response  to  their  demands  the  optician  increased  his 
angles  and  working  force  of  the  object-glasses.  To  meet 
this  in  turn  called  for  the  construction  of  condensers  of 
greater  angle;  until  finally  it  occurred  that  the  aper- 
ture of  the  objective  had  arrived  at  proportions  to 
which  the  condensers  did  not  satisfactorily  respond. 
Something  had  to  be  done,  and  something  was  done, 
for  necessity  is  the  "  mother  of  invention." 

The  simplest  way  is  the  best,  and  this  was  to  reduce 
the  thickness  of  the  stage.  The  "fighter"  of  objec 
tives  had  discovered  the  fact  that  a  stage,  one-fifth  of  an 
inch  in  thickness,  was  solid  enough  for  any  and  all  of 
the  delicate  work  required  by  the  microscopist,  while  at 
the  same  time  he  derived  a  great  advantage  in  thus  pro- 
viding play  for  the  aperture  of  his  objectives. 

The  writer  remembers  with  pride  that  he  "  took  a 
hand""  at  this;  he  remembers,  too,  the  unalloyed  satis- 
faction he  experienced  in  seeing  two  heavy,  lumbering, 
and  expensive  stages,  alone  costing  several  hundred  dol- 
lars, removed  from  imported  stands,  and  their  place 
substituted  by  plain,  thin  plates  made  by  the  local 


20  HOW   TO    SEE   WITH   THE   MICROSCOPE. 

watchmaker;  he  recollects,  also,  the  exclamation  of 
one  of  his  friends,  after  looking  at  an  object  as  dis- 
played by  the  improvised  stage :  "  Well,  I  declare ! 
This  instrument  was  made  for  any  thing  in  creation  but 
to  see  through." 

Hence  it  was,  responding  to  the  increasing  call,  our 
American  and  London  makers  decreased  the  thickness 
of  their  stages.  While  it  is  yet  true  that  many  of  the 
present  stages  are  unnecessarily  thick,  the  reduction  is 
still  palpably  manifest. 

It  may  be  remarked,  then,  that  the  real  improvement 
of  late  years  in  the  construction  of  American  and  Lon- 
don stands  may,  as  a  rule,  be  manifested  in  these  two 
items,  viz.,  reduction  of  weight  and  thickness  of  stage. 

We  have  learned  something  from  the  Germans,  too, 
within  the  past  few  years.  It  has  been  well  known 
that  they  favored  the  vertical  stand  with  its  short  tube. 
Our  experience  has  taught  us  that  both  of  these  have 
their  advantages,  and  our  later  instruments  are  so  con- 
trived as  to  be  used  with  short,  and  also  with  standard 
tube,  and  in  a  vertical  or  inclined  position. 

I  desire  in  this  place  to  record  the  fact  that  the  stands 
made  in  the  United  States  are  not  excelled  in  any  qual- 
ity or  condition  going  to  make  a  number  one,  reliable 
instrument.  ^The  stands  produced  by  our  home  makers 
are  quite  equal  in  every  respect  to  those  of  any- other 
countries,  while  their  cost  is  not  one  whit  higher. 

Those  contemplating  the  purchase  of  a  stand  will,  as 
a  matter  of  course,  consult  their  individual  taste  and 
inclinations  to  a  considerable  extent :  thus,  A  may  select 


SOMETHING    ABOUT    AMERICAN    STANDS,    ETC.  21 

a  large  and  heavy  stand,  while  B  would  prefer  a  smaller 
and  lighter  one.  The  party,  too,  will  naturally  take 
into  consideration  the  particular  field  of  work  he  may 
have  in  contemplation.  It  is  quite  possible  to  give  the 
latter  consideration  too  much  weight.  It  will  be  found, 
as  a  rule,  better  policy  in  the  long-run  to  purchase  a 
stand  capable  of  doing  almost  any  work,  and  thus  avoid 
the  possibility  of  being  compelled  to  sell  at  some  future 
date,  at  a  heavy  discount,  and  purchase  another  and 
more  capable  stand.  Fortunate  it  is  that  one  can  now 
purchase,  at  moderate  figures,  reliable  and  well-made 
stands,  suitable  for  almost  any  purpose  of  tl  e  micro- 
scopist. 

In  the  reference  that  has  been  made  to  American 
stands,  it  is  proper  to  state  that  the  Messrs.  Beck,  of 
London,  have  a  regular  agency  here  for  the  sale  of 
their  wares,  and  that  this  agency  is  in  charge  of  an 
American  gentleman.  There  can  be  no  good  reason  to 
regard  them  as  other  than  home  folks.  At  all  events, 
the  author  is  of  this  opinion,  and  will  act  accordingly. 

Among  the  essentials  that  deserve  attention  in  the 
selection  of  a  reliable  stand  may  be  mentioned  : 

FIRST.  See  that  the  stand  is  well  balanced  in  every 
position  that  it  manifests  no  disposition  to  topple 
either  one  way  or  the  other;  that  it  stands  tolerably 
firm  (for  its  weight)  on  its  legs. 

SECOND.  If  it  has  coarse  adjustment  by  rack  and 
pinion,  see  that  the  movement  is  as  smooth  as  oil; 
reverse  the  milled  heud  between  the  thumb  and  finger 
promptly,  and  notice  if  there  be  any  lost  motion;  try 


22  HOW    TO   SEE    WITH   THE   MICROSCOPE. 

this  test  all  the  way  of  the  "run"  of  the  rack,  and  if 
there  be  "  lost  motion"  detected  discard  the  stand. 

THIRD.  Examine  carefully  the  bearings  on  which 
the  body  slides;  these  should  be  broad,  and  the  fitting 
of  the  body  to  the  limb  accurate;  test  by  placing  a 
small  object  on  the  stage — a  circular  diatom  will  be  the 
thing;  now  examine  with  a  half-inch  glass;  rack  the 
tube  up  and  down  a  little,  and  see  if  the  object  keeps 
its  centre ;  seize  the  body-tube  near  the  eye-piece,  and 
twist  it  a  bit  from  right  to  left,  and  vice  versa,  noticing 
whether  the  object  "travels"  or  not;  repeat  this  ex- 
periment by  punching  holes  in  a  card-box,  say  three- 
quarters  of  an  inch  thick,  thus  forming  a  supplemental 
stage ;  focus  again  and  try  the  twist  once  more.  The 
instrument  that  will  stand  this  test  is  all  right  as  to  its 
bearings. 

FOURTH.  Place  the  diatom  on  the  stage,  under  the 
half-inch,  as  before,  and  if  the  instrument  has  fine  ad- 
justment by  nose-piece,  test  by  moving  the  fine  wheel 
quickly  either  way,  and  see  if  the  object  "  travels."  If 
satisfactory  with  the  half-inch,  try  an  eighth,  or  tenth ; 
test  also  by  taking  hold  of  the  objective  as  one  would 
in  the  adjustment  for  cover,  by  giving  it  a  little  twist 
right  and  left,  and  see  if  the  object  changes  its  position. 
Finally,  examine  the  run  of  the  fine  adjustment;  see  if 
it  is  quick  and  sensitive  to  the  touch,  without  "jump;" 
if  satisfactory  so  far,  so  good. 

FIFTH.  Should  the  stand  have  concentric  stage,  test 
the  accuracy  of  its  fittings  with  diatom  and  half-inch 
glass.  If  the  stand  has  suffered  transportation,  or  has 


SOMETHING   ABOUT   AMERICAN   STANDS,    ETC.  23 

in  any  way  been  submitted  to  fatigue,  the  probability 
will  be  that  the  stage  has  become  somewhat  decentred, 
and  any  effort  of  your  own  to  re-adjust  will  be  likely  to 
make  things  worse.  The  very  best  stages  will  not 
remain  centred  long  if  roughly  used.  Still,  with  your 
half-inch  and  the  diatom  you  can  manage  to  get  some 
idea,  which  will  be  better  than  none  at  all.  Centre 
your  diatom,  and  focus;  now  seize  opposite  edges  of 
the  stage  with  both  hands,  hold  it  firmly,  giving  it 
"jerks"  either  way,  right  and  left,  but  not  sufficiently 
to  absolutely  move  the  stage  on  its  centre.  If  you  suc- 
ceed in  moving  your  object,  with  a  corresponding  move- 
ment of  the  stage,  then  the  latter  is  not  accurately 
fitted,  and  cannot  be  accurately  centred.  This  "slip" 
can  be  detected  with  the  hands  alone. 

SIXTH.  It  the  stand  be  furnished  with  mirror  fitted 
to  radial  arm,  see  that  all  these  fittings  are  strong  and 
likely  to  last.  This  portion  of  the  stand  meets  with 
more  fatigue  than  any  other.  See  that  the  friction  sur- 
faces are  not  both  the  same  metal ;  this  will  apply,  too, 
to  any  part  of  the  stand.  Notice  particularly  whether 
the  universal  motions  of  the  mirror  are  properly  con- 
structed, and  likely  to  last  for  years;  this  is  a  most  im- 
portant point. 

FINALLY.  It  will  be  well  to  see  that  the  joint  for 
inclining  the  instrument  at  various  angles  is  strong  and 
well  made,  and  that  it  have  compensation  for  wear. 
Notice  the  general  "  get  up"  — the  general  finish  of  its 
various  parts.  And  now,  having  received  a  lesson  on 
the  use  of  diatoms,  you  may  put  the  little  fellow  away 
until  again  wanted. 


24  HOW   TO   SEE   WITH   THE   MICROSCOPE. 

Aside  from  these  matters  involving  sound  mechanism, 
there  remain  other  points  connected  with  the  choice  of 
a  stand,  which  may,  to  some  extent,  be  regarded  as  a 
matter  of  election.  For  instance,  some  of  the  most 
costly  stands  are  furnished  with  mechanical  stages 
whereby  motions  are  given  to  the  object-carrier  by 
various  milled  heads.  I  have  used  these  stages  in  times 
past,  anc1  have  to  record  my  disapprobation  of  them, 
and  for  the  following  reasons : 

FIRST.  They  are  an  impediment  to  quick  work.  It 
is  much  quicker  to  run  from  one  end  of  an  object  to 
another  by  one  single  movement  given  by  hand  than 
to  wait  the  slow  motions  of  the  screws.  There  are,  how- 
ever, some  advantages  arising  at  times  from  the  use  of 
the  mechanical  staore,  e.  g.,  in  adjusting  the  image  of  an 
object  to  the  eye-piece  micrometer,  etc.  Nevertheless 
these  slight  conveniences  are  sadly  outweighed  by  the 
positive  objection  to  their  use. 

SECOND.  A  mechanical  stage,  to  be  good  for  any 
thing  must  be  nicely  made ;  hence  they  are  costly,  and 
further,  seldom  keep  in  order  for  a  great  length  of  time, 
however  well  made. 

THIRD.  As  generally  modelled,  they  increase  the 
thickness  of  the  stage,  and  the  screws  are  always  more 
or  less  in  the  way. 

FOURTH.  Those  who  rely  on  their  mechanical  assist- 
ance seldom  arrive  at  that  delicate  finger  manipulation 
so  necessary  to  be  acquired  by  the  observer.  Any  one 
of  the  objections  above  named  ought,  in  my  opinion,  to 
1x3  sufficient  and  determinate. 


SOMETHING   ABOUT   AMERICAN   STANDS,    ETC.  25 

Many  of  the  first-class  stands  (so  called)  are  fitted 
with  sub-stages,  provided  with  rack  and  pinion,  and 
•centering  screws.  In  the  latter  models  these  accessories 
<?an  be  completely  removed,  leaving  the  entire  instru- 
ment below  the  stage  clear  and  unobstructed.  Beyond 
the  cost  which  these  appliances  incur,  I  see  no  particu- 
lar objection  to  their  presence ;  but  the  novice  is  in- 
formed that  they  are  by  no  means  a  necessary  adjunct, 
iind  that  their  duties  can  be  performed  by  simple  and 
less  costly  contrivances. 

Stands  have  lately  been  introduced  with  short  tubes, 
but  capable,  by  means  of  an  interior  draw,  of  being 
•drawn  out  to  the  standard  length  of  ten  inches.  This 
is  an  improvement  on  the  short  tube  of  the  German 
school,  and  one  of  real  value.  The  daily  worker  will 
find  the  short  tube  a  great  convenience  when  working 
over  wet  preparations,  or  dealing  with  reagents.  Under- 
these  circumstances,  to  work  quickly  one  must  needs 
keep  the  stage  horizontal  and  the  tube  vertical.  It  is 
true  that  we  can  compensate,  in  a  measure,  in  using  the 
standard  lengths  by  working  with  a  lower  table ;  but 
in  this  case  the  observer  cannot  have  his  instrument  so 
well  under  control,  and  he  is  further  compelled  to  re- 
sort to  some  out-of-the-way  contrivance  by  way  of  get- 
ting rests  for  the  elbows. 

In  the  selection  of  a  stand,  I  advise  strongly  that  it 
be  fitted  with  a  concentric  rotating  stage ;  and  should 
the  res  angusta  domi  present  no  obstacle,  let  the  stage 
be  a  good  one,  divided  to  degrees,  capable  of  an  entire 
revolution,  and  furnished  with  an  object-carrier.  The 


26  HOW    TO    SEE    WITH   THE   MICROSCOPE. 

advantages  ot  the  revolving  stage  are  manifold,  while 
to  the  advanced  worker,  it  is  a  sine  qua  non.  In  the 
examination  of  difficult  and  resisting  structures  the  ob- 
server needs  at  times  to  employ  almost  every  variety  of 
illumination,  as  well  as  to  view  the  object  under  various- 
aspects.  In  this  department  of  work  the  rotating  stage 
cannot  be  dispensed  with. 

Where  money  is  an  object,  let  the  would-be  purchaser 
proceed  with  due  care,  giving  this  matter  the  closest 
attention.  By  observing  the  following  instructions  he 
can  provide  for  a  rotating  stage  capable  of  responding 
to  almost  any  call,  and  at  an  outlay  not  to  exceed  five 
dollars.  The  writer  has  two  stands.  One  is  a  large, 
heavy,  first-class  instrument,  and  is,  of  course,  furnished 
with  adjusting  concentric  stages,  divided  to  half-degrees ; 
the  other  is  one  of  the  smallest  stands  made,  and  is- 
fitted  with  short  tube  (which  can  be  drawn  out  to 
standard  length),  and  a  plain,  revolving  stage,  which 
cost  two  dollars.  Ninety-five  per  cent,  of  all  his  work 
is  done  on  the  little  stand;  the  work  allotted  to  the 
larger  instrument  being  the  measurement  of  the  angles 
of  crystals,  recording  of  objects  by  the  Maltwood  finder,, 
and  the  measurements  of  the  angular  aperture  of  ob- 
jectives. This  much  for  the  solace  of  those  who  are 
bothered  with  the  hard  times. 

In  making  the  selection  with  the  view  in  hand  of 
providing  a  cheap  rotating  stage,  the  first  important 
point  is  to  see  that  the  instrument  has  sufficient  stage 
room.  The  stage  should  measure  one  and  seven-eighth 
inches  from  the  centre  of  well-hole  to  the  nearest  por- 


SOMETHING   ABOUT   AMERICAN    STANDS,    ETC.  27 

tion  of  the  limb  touching  the  stage ;  and  any  instrument 
having  less  distance  than  this  will  not  answer  for  the 
purpose,  while  a  half-inch  more  room  would  be  very 
desirable.  The  object  of  all  this  is  to  get  room  enough, 
so  that  we  can  employ  a  circular  stage  large  enough  to- 
work  an  object-carrier. 

Next,  see  that  there  are  no  sub-stage  fittings,  which, 
by  their  paiticular  method  of  attachment,  will  inter- 
fere with  the  stage  about  to  be  described.  Look  the 
ground  over  carefully,  and,  accepting  that  the  road  i& 
all  clear,  we  proceed  to  describe  the  stage  which  the 
aulhor  has  had  in  daily  use  for  years,  and  one  that  has,, 
to  a  considerable  extent,  been  copied  by  his  friends. 
Any  watchmaker  or  machinist  can  do  the  work — in 
fact,  one  of  my  friends  made  one  for  himself. 

Provide  a  sheet  of  well-hammered  brass,  heavy  enoughr 
so  that  when  planed  or  turned  down  the  stage  shall  be 
one-sixteenth  of  an  inch  in  thickness,  with  both  faces 
truly  parallel.  Cut  the  circle  which  is  to  form  your 
stage  as  large  as  your  instrument  will  permit,  and  in 
accordance  with  the  above  directions. 

Cut  the  well-hole  one-sixteenth  of  an  inch  larger 
than  the  W3ll-hole  of  your  stage;  make  a  collar,  or 
short  tube,  out  of  the  same  material  used  for  the  stage; 
turn  the  outside  to  proper  dimensions,  so  as  to  fit  the 
well-hole  of  the  new  stage,  the  upper  edges  of  both 
being  "  flush,"  and  solder  in  position. 

Next:  Turn  accurately  the  under  and  projecting  part 
of  the  short  collar,  or  tube,  so  that  it  will  exactly  fit 
the  well-hole  of  your  main  stage ;  place  it  thereon,  and 


28  HOW   TO   SEE    WITH   THE   MICROSCOPE. 

cut  off  any  portion  of  the  collar  that  may  project 
beneath  said  stage. 

In  the  stage  thus  far  towards  completion,  it  so  be 
that  the  collar  projects  one-sixteenth  of  an  inch,  this 
will  be  found  ample  for  its  support ;  thus  you  will  be 
enabled  with  some  stands  to  steer  clear  of  sub-stage 
appliances,  etc. 

All  that  remains  to  be  done  is  to  fit  your  new  stage 
with  plain  spring-clips,  which  can  be  done  in  a  few 
moments  out  of  a  piece  of  watch-spring;  or,  if  there  is 
room  enough,  you  can  provide  an  object-carrier,  made 
on  Mr.  Zentmayer's  principle;  all  of  which  is  plain 
work,  and  easily  accomplished  by  any  machinist  of  toler- 
able skill. 

Keep  in  mind  that  this  stage  adds  somewhat  to  the 
thickness,  and  govern  yourself  accordingly. 

"  But,"  says  one,  "  I  have  no  assurance  that  this  stage 
will  rotate  in  the  optical  axis."  I  grant  it,  with  the 
remark  that  if  it  did  so  rotate  with  one  objective,  it 
would  be  pretty  sure  to  fail  with  another.  The  com- 
pensation must  be  supplied  by  finger  manipulations, 
•easily  acquired,  and  as  easily  practiced.  As  I  have 
previously  hinted,  the  best  rotating  stages  remain  con- 
centric but  fora  short  time,  especially  if  much  used; 
while  to  the  real  worker,  the  very  bother  of  adjusting 
the  most  expensive  stage  extant  would  be  an  intolerable 
annoyance,  and  a  willful  waste  of  time. 

A  grand  good  thing  about  this  improvised  stage  is, 
that  it  can  be  placed  in  position  or  removed  therefrom 
in  a  moment's  time.  This,  to  the  author,  is  a  real  boon, 


SOMETHING    ABOUT   AMEKICAN    STANDS,    ETC.  29 

for  he  has  often  to  remove  the  supplemental  stage,  and 
to  work  for  hours  with  the  mounts  placed  on  the  main 
plate,  using  not  even  the  spring-clip  or  any  other 
attachment,  the  microscope  being  the  while  in  the  ver- 
tical position. 

Says  another:  Why  not  have  the  maker  furnish 
some  such  stage  at  the  date  of  purchase  ?  He  can  do- 
these  things  better  than  any  one  else."  I  respond,, 
Yea,  verily. 

Thousands  of  times  the  question  has  been  asked,. 
44  Which  do  you  prefer — the  binocular  or  the  monocu- 
lar? "  and  as  it  is  more  than  probable  that  this  question 
will  arise  in  the  minds  of  some  of  those  who  read  thia 
book,  perhaps  a  word  or  two  on  the  subject  may  not  be 
amiss. 

Mr.  Henry  Crouch,  F.  K.  M.  S.,  a  well  known  maker 
of  microscopes,  visited  this  country  during  the  Centen- 
nial Exhibition,  and  on  his  return  complained  bitterly 
of  "an  eminent  German  microscopist,  who  assisted  in 
examing  the  microscopes  on  exhibition  at  Philadelphia, 
and  who  from  the  first  loudly  proclaimed  the  useless- 
ness  of  binoculars,  .  .  .  but  whom  he  afterwards 
found  out  had  never  used  one."  The  author  is  pretty 
much  in  the  same  boat  with  the  eminent  German. 

Since  the  introduction  of  the  binocular,  the  writer 
has  made  several  downright  square  and  honest  attempts 
to  use  the  binocular  long  enough  to  be  able  to  express 
an  opinion  worth  consideration,  but  in  each  and  every 
case  the  double  barrelled  machine  proved  too  much  for 
his  patience.  With  the  low  powers  the  instrument  i& 


•30  HOW    TO    SEE    WITH   THE   MICROSCOPE. 

capable  of  giving  very  pretty  shows,  particularly  where 
a  certain  stereoscopic  effect  is  supposed  to  add  force. 
Hence  the  binocular  is  eminently  fitted  for  such  dis- 
plays, and  is  eminently  adapted,  too,  for  the  entertain- 
ment of  those  of  our  lady  friends  who  visit  the  soirees 
of  microscopical  societies,  without  feeling  specially 
interested  in  microscopy  as  a  science. 

If  so  be  that  there  can  be  structure  displayed  by  the 
binocular  that  cannot  be  seen  equally  well  by  the  mon- 
ocular, be  it  so,  and  the  author  will  joyfully  add  his 
testimony  to  the  same,  after  having  arrived  at  the  fact. 

Many  of  my  friends  have  binocular  instruments,  but 
I  can  not  recall  the  name  of  any  person  who  uses  one ; 
that  is,  when  I  am  present,  for  inevitably  the  first  thing 
done  by  the  owner  is  to  displace  the  prism,  and  to  use 
the  stand  as  a  monocular.  I  have  never  found  a  soli- 
tary exception  to  this  rule. 

But  some  one  may  say:  "  What  possible  objection  can 
there  be  to  purchasirg  a  binocular,  since,  as  you  admit, 
the  instrument  can  be  changed  instantly  to  a  monocu- 
lar, and  the  purchaser  has  his  choice.  He  certainly  has 
nil  that  you  have  got,  and  perhaps  (allowing  force  to 
the  opinion  of  others)  more  too." 

Well,  that  looks  lucid  enough;  and  in  truth  that 
argument  has  sold  many  a  binocular.  Nevertheless, 
"  all  is  not  gold  that  glitters."  Let  us  take  a  look  from 
another  stand  point,  thus : 

First.  The  binocular  involves  greater  weight ;  as  a 
rule,  they  are  unwieldly,  lumbering  things,  destitute  of 
grace,  symmetry,  or  aught  that  goes  to  make  a  clean, 
well  proportioned  stand. 


SOMETHING    ABOUT   AMERICAN    STANDS,    ETC.  31 

Second.  The  binocular  instrument  is  much  more 
complicated,  and  hence  more  expensive,  the  purchaser 
~being  required  to  pay,  without  getting  in  return  value 
received. 

Third.  This  form  does  not  admit  of  the  instrument 
being  used  with  short,  as  well  as  standard  tube,  and  to 
the  "  worker  "  this  item  has  particular  force. 

Fourth.  The  extra  expense  attending  the  purchase 
•of  a  binocular  can  be  better  applied  in  other  directions. 
Those  who  value  dollars  and  cents  will  find  force  in 
'this  objection. 

Fifth.  I  oppose  the  binocular,  because  the  monocu- 
lar is  good  enough,  and  because  the  real  work  of  the 
microscope  has  been  and  will  continue  to  be  done  with 
the  monocular. 

Sixth.  The  binocular  is  to  a  certain  extent  impract- 
icable, because  the  two  eyes  of  the  observer  are  not 
alike.  There  are  exceptions,  but  not  to  an  extent  suffi- 
cient to  invalidate  the  rule. 

Seventh.  I  oppose  the  usual  form  of  binocular 
instruments,  believing  that  the  binocular  eyepiece 
invented  and  made  by  Mr.  K.  B.  Tolles  is  a  preferable 
way  of  obtaining  binocular  vision. 

Having  thus  presented  my  objections,  let  the  reader 
elect  for  himself,  with  this  assurance  on  my  part,  viz., 
better  get  a  good  binocular  than  a  poor  monocular. 

All  stands  should  be  furnished  with  plane  and  con- 
cave mirrors.  If  the  mirrors  are  attached  to  radial  arm, 
hinged  at  a  greater  or  less  distance  from  the  under  sur- 
face of  the  stage,  then  it  is  apparent  that  when  the 


32  HOW   TO    SEE   WITH   THE   MICROSCOPE, 

radial  arm  is  placed  in  position  for  oblique  light  the 
mirror  will  be  nearer  the  well  hole  than  when  the  arm 
is  centrally  disposed ;  therefore,  the  mirror  should  be 
arranged  to  slide  on  the  arm,  so  that  the  proper  com- 
pensation may  be  effected. 

The  mirror  should,  of  course,  be  well  mounted  in  its 
own  semicircular  arm,  so  that  universal  motions  may  be- 
obtained,  and  the  semicircle  should  be  closely  attached 
to  the  slide  moving  on  the  radial  arm ;  that  is  to  sayy 
there  should  be  no  intermediate,  short,  and  jointed  arm^ 
or  elbows  such  as  are  found  on  many  so-called  first 
class  instruments,  and  are  a  most  intolerable  nuisance. 
It  is  quite  possible  at  times  to  remove  these  intermedi- 
ate arms,  and  attach  the  mirrors  directly  to  the  radial 
arm,  and  at  a  trifling  expense,  thus  transforming  a 
faulty  stand  into  a  really  serviceable  one. 

Examine  the  concave  mirror  carefully,  as  to  its  local 
length.  To  do  this,  place  a  piece  of  white  letter  paper 
on  the  stage,  and  using  a  common  candle  reflect  the 
light  on  the  paper ;  now  move  the  mirror  up  and  down 
on  the  radial  arm,  and  see  if  you  can  get  a  tolerably 
well  defined  image  of  the  flame.  It  may  occur  the 
radial  arm  is  too  short  for  the  focal  length  of  the 
mirror,  and  that  it  would  be  impossible  to  lengthen  it 
sufficiently;  this  being  the  case,  reject  the  stand. 

One  would  naturally  suppose  that  an  item  like  the 
last  would  surely  be  attended  to  on  the  part  of  the 
maker;  nevertheless,  many  stands  are  made  and  sold 
with  glaring  defects  of  this  character. 

At  the  risk  of  being  tiresome,  let  me  especially  insist 


SOMETHING   ABOUT   AMERICAN   STANDS,   ETC.  33 

on  the  absolute  importance  of  looking  carefully  to  the 
entire  apparatus  connected  with  the  hanging  of  the 
mirrors.  This  part  of  the  mechanism  is  called  to 
endure  more  fatigue,  and  is  ottener  thus  called  on  than 
any  other  portion  of  the  stand.  For  instance :  In  the 
act  ot  observing,  one  often  has  occasion  to  seize  the 
mirror,  and  to  move  it  and  the  radial  arm  by  a  single 
impulse,  simultaneously  as  it  were;  and  here  let  me  say 
that  it  will  be  well  for  the  observer  to  acquire  this 
habit;  nevertheless,  it  is  terribly  straining  on  the 
joints  thus  called  on,  and  they  should  be  strong  enough 
to  endure  the  fatigue. 

See  also  that  all  the  eye  pieces  slip  in  and  out  of  the 
tube  easily;  this  too  without  decentring  the  object  in 
the  field.  Any  difficulty  in  putting  eye  pieces  in  place 
or  removing  therefrom  is  a  first  class  botheration. 

We  now  proceed  to  the  description  of  the  stands 
made  and  sold  by  American  makers.  In  placing  Mr. 
Joseph  Zentmayer  at  the  head  of  this  list,  the  author 
feels  assured  that  he  does  no  violence  to  the  feelings  of 
others.  Mr.  Zentmayer  was  one  of  our  earliest  and  most 
energetic  makers,  and  his  work  has,  as  a  rule,  proved 
honest  and  reliable.  In  his  expenditure  of  capital,  his 
facilities  for  execution,  or  his  pride  in  presenting  first- 
class  work,  he  stands  second  to  none,  as  his  competitors 
will  generally  attest. 

Mr.  Zentmayer's  largest  and  most  costly  stand  has,  I 
may  say,  but  just  been  placed  on  the  market.  It  was 
especially  designed  for  exhibition  at  the  Centennial 
Exposition.  The  description  which  follows  is  to  a  con- 


34  HOW  TO   SEE   WITH  THE   MICROSCOPE. 

siderable  extent  the  same  as  that  printed  in  Mr.  Zent- 
mayer's  catalogue  —  some  portions  being  suppressed, 
and  the  wording  occasionally  changed  at  the  election  of 
the  author.* 

ZENTMAYER'S  AMERICAN  CENTENNIAL  STAND. 

Constructed  especially  for  the  Centennial  Exhibition. 
It  is  mounted  on  a  tripod,  with  revolving  graduated 
platform  ;  the  bar  and  trunnions  are  in  one  piece,  and 
swing  between  two  pillars  for  inclining  the  instrument 
to  any  angle.  The  coarse  adjustment  is  accomplished 
by  rack  and  pinion.  Thus  far  it  is  similar  to  the 
"  Grand  American  Stand"  by  the  same  maker. 

The  swinging  sub-stage,  which  carries  the  condenser 
or  other  illuminating  apparatus,  including  the  mirror, 
swings  around  a  pivot,  the  axis  ot  which  passes  through 
the  object  observed,  so  that  this  object  is  in  every  posi- 
tion in  the  focus  of  illumination.  The  stage  may  be 
detached  with  facility,  and  replaced  by  one  constructed 
for  oblique  illumination;  the  swinging  illuminator 
may  then  (i.  e.,  with  the  last-named  stage)  be  used  for 
illumination  from  above. 

The  sub-stage  is  provided  with  a  graduated  circle  for 
indicating  the  degree  of  obliquity. 

An  object  placed  on  the  stage  being  in  a  plane  with 
the  axis  of  the  trunnions,  it  is  obvious  that  if  the  in- 
strument is  placed  in  a  horizontal  position,  the  object 

*In  the  several  descriptions  of  stands,  that  of  the  respective  makers  will 
be  given  as  far  as  possible.  The  author  will,  however,  at  his  election,  sup- 
nress  certain  portions  or  change  the  diction  as  to  him  may  appear  desirable. 


ZENTMAYER'S  AMERICAN  CENTENNIAL  STAND.        37 

is  in  the  axis  of  revolution  of  the  graduated  platform, 
and  the  angular  aperture  of  an  objective  focused  on  this 
object  can  easily  be  measured.  It  is  equally  obvious 
that  in  this  position  the  object  is  in  the  centre  of  all 
the  revolving  parts  of  the  instrument,  to  wit,  the  re- 
volving stage,  swinging  sub-stage,  and  the  platform. 

The  principal  stage  is  similar  to  the  circular  one  pre- 
viously used  on.  the  "  Grand  American;"  it  is  provided 
with  adjusting  screws  for  accurate  centring,  and  re- 
volves in  a  large  outside  ring,  giving  facilities  for 
oblique  illumination  up  to  70  degrees  from  axis  (140 
degrees  aperture),  while  the  graduations  serve  as  a 
goniometer  for  the  measurement  of  crystals,  etc. 

The  sub-stage  is  divided  into  two  cylindrical  receivers, 
to  facilitate  the  adaptation  of  several  accessories  at  one 
and  the  same  time ;  the  lower  cylinder  can  be  moved  up 
and  down  or  entirely  removed. 

The  fine  adjustment  (in  all  other  instruments  of  the 
Jackson  model  being  in  front  of  the  body)  is  removed 
to  the  more  stable  part  of  the  stand.  The  bar  is  pro- 
vided with  two  slides,  one  for  the  rack  and  pinion 
movement,  and  close  to  it  another  one  of  nearly  the 
same  length  for  the  fine  adjustment,  moved  by  a  lever 
concealed  in  the  bent  arm  of  the  bar,  and  acted  on  by  a 
micrometer  screw.  Thus  the  body  is  not  touched  when 
using  the  fine  adjustment,  and  the  relative  distances  of 
objective,  binocular  prism  and  eye-piece  remain  un- 
changed. 

The  smaller  stage  of  the  American  Centennial  Stand 
is  also  provided  with  screws  for  accurate  centring ;  this 


38  HOW   TO    SEE    WITH  THE   MICROSCOPE. 

stage  is  three  inches  in  diameter  and  extremely  thin, 
allowing',  in  connection  with  the  swinging  sub-stage 
and  mirror,  not  only  the  greatest  obliquity  of  illumina- 
tion, but  the  mirror  and  achromatic  condenser  will  rise 
above  the  stage  when  required,  as  in  the  case  of  sun- 
light illumination,  that  of  opaque  objects,  etc. 

The  diameter  of  the  sub-stage  is  the  same  as  that  of 
the  "  Grand  American;"  the  accessories  of  that  stand 
are  therefore  interchangeable. 

As  to  the  general  character  of  Mr.  Zentmayer's  work, 
the  author  «an  affirm  with  confidence  that  it  is  not  ex- 
celled in  any  particular.  The  stand  just  described  is 
beautiful  in  design,  is  nicely  proportioned,  and  in  every 
repect  reliable  and  durable.  It  will  stand  all  of  the 
tests  named  in  the  preceding  pages.  Those  wishing  a 
first-class  stand  cannot  fail  to  be  satisfied  with  the  Cen- 
tennial. 

The  swinging  sub-stage  carrying  the  mirror,  etc.,  is  a 
most  valuable  improvement,  and  one  that  the  observer 
can  hardly  afford  to  be  without;  the  mechanism,  too, 
by  which  this  end  is  accomplished  is  of  the  strongest 
and  most  workman-like  order. 

Attention  also  is  invited  to  the  method  of  attachment 
of  the  stage.  The  latter  is  solidly  held  in  position,  or 
can  in  a  moment  be  detached,  and  another  stage  substi- 
tuted. 

It  has  occurred  to  the  writer  that  the  "  principal 
stage"  mentioned  might  very  well  be  dispensed  with 
the  smaller  stage  being  quite  sufficient.  Possibly  a  large 
and  plain  stage  might  at  times  be  found  a  convenience, 


THE   AMERICAN   HISTOLOGICAL    STAND.  39 

this  could  easily  be  substituted  for  the  more  expensive 
one  furnished  with  the  instrument. 

As  to  the  smaller  stage  referred  to,  the  author  can 
"  speak  by  the  card."  He  had  used  one  of  Mr.  Zent- 
mayer's  army  hospital  stands  for  years,  and  the  instru- 
ment gave  him  good  satisfaction.  Two  years  ago,  how- 
ever, desiring  a  thinner  and  a  revolving  stage,  he  begged 
Mr.  Zentmayer  to  devise  one  and  fit  the  same  to  his 
stand.  Quite  a  correspondence  ensued,  and  the  army 
stand  was  thus  equipped,  the  new  stage  being  practic- 
ally the  same  as  the  small  one  furnished  with  the  Cen- 
tennial. It  worked  nicely,  and  was,  in  truth,  all  that 
the  author  desired. 

In  the  change  of  stages  proposed,  attention  is  called 
to  the  fact  that  the  smaller  stage  has  not  the  graduated 
edge.  This  to  the  majority  of  users  would  not  be  a 
serious  objection,  while,  on  the  contrary,  many  would 
gladly  avoid  the  cost  of  the  graduated  circle. 

Mr.  Zentmayer  makes  some  eight  or  nine  different 
forms  of  stands.  We  have  room  to  describe  only  one 
other,  viz. : 

THE   AMERICAN   HISTOLOGICAL    STAND. 

The  requirements  held  in  view,  in  the  construction 
of  this  little  instrument,  were  the  combining  of  the 
facilities  of  a  first-class  stand  with  moderate  cost. 

The  entire  instrument  is  made  of  brass,  the  base  and 
uprights  are  one  piece,  of  a  peculiar  shape,  and  of  great 
rigidity,  to  which  the  bell-metal  bar  is  attached  by  a 


42  HOW  TO   SEE   WITH  THE   MICROSCOPE. 

joint,  allowing  the  use  of  the  instrument  at  any 
of  inclination;  perpendicular  and  horizontal  positions 
are  indicated  by  stops ;  the  coarse  adjustment  is  accom- 
plished by  a  sliding  tube,  the  tube  being  but  five  and 
one-half  inches  long,  but  capable  of  elongation  to  the 
standard  length. 

The  fine  adjustment  is  similar  to  that  of  the  Centen- 
nial —  a  concealed  lever  moving  the  entire  body ;  this 
adjustment  is  reliable  and  very  delicate.  The  sub-stage, 
plane  and  concave  mirrors,  swing  in  the  same  manner  as 
do  those  of  the  Centennial,  having  the  object  in  its 
centre,  even  when  swung  over  the  stage. 

The  sub-stage  carries  the  diaphragms,  of  which  three 
are  furnished  with  the  instrument.  Any  piece  of  sub- 
stage  apparatus,  such  as  condensers,  paraboloids,  prisms, 
in  fact  anything  from  the  lists,  can  legitimately  be 
adapted  to  the  sub-stage,  or  the  same  can  be  instantly 
removed,  with  the  mirror  also,  if  desired,  thus  leaving 
the  stand  free  from  any  obstruction  below  the  stage. 

The  sub-stage  slides  up  and  down  in  strong  dovetailed 
grooves,  and  has  centering  adjustments  by  hand.  The 
weight  of  this  little  stand  I  judge  to  be  about  three  or 
four  pounds;  it  can,  on  a  pinch,  be  carried  in  one's 
great-coat  pocket. 

It  is  worthy  of  mention  in  connection  with  these  two 
stands  of  Mr.  Zentmayer's,  that  the  fine  adjustment 
has  been  removed  from  the  front  to  the  rear,  or,  as 
Mr.  Zentmayer  says,  "  to  the  more  stable  part  of  the 
instrument."  The  author,  when  his  attention  was  first 
called  to  these  stands,  regarded  this  change  of  the  fine 


THE   AMERICAN   HISTOLOGICAL    STAND.  43 

adjustment  as  one  of  doubtful  utility;  and  he  once 
made  the  remark  to  a  friend,  that  should  he  purchase  a 
Centennial,  he  should  insist  that  the  maker  furnish  a 
fine  adjustment,  both  front  and  rear. 

Certain  it  is  that,  in  the  process  of  correcting  a  first- 
class  wide-angled  objective,  it  is  a  convenience  to  have 
the  fine  adjustment  at  the  Iront.  It  is,  however,  ex- 
ceedingly, difficult  to  so  accurately  fit  the  sliding  nose- 
piece  that  it  shall  move  up  and  down  with  perfect  free^ 
dom  when  acted  upon  by  the  fine  screw,  and  at  th( 
same  time  to  be  free  from  lateral  motion,  and  this 
lateral  motion  constitutes  a  first-class  fault  to  which 
the  attention  of  the  reader  has  been  called  on  another 
page.  The  very  best  makers  have  found  it  difficult  to 
steer  clear  of  this.  The  writer  once  met  with  one  of 
Mr.  Zentmayer's  larger  stands  exhibiting  this  defect  in 
a  marked  degree.  His  own  "  Grand  American  Stand,'' 
however,  in  this  respect,  is  faultless. 

Thus  it  will  be  seen  that,  in  the  nature  of  things,  a 
really  fine  adjustment  acting  on  the  nose-piece  involves 
skilled  labor,  and  this,  in  turn,  involves  cost. 

Again,  the  movable  nose-piece  necessarily  changes 
the  length  of  the  body-tube,  and  this,  in  turn,  again, 
changes  the  amplifying  power  of  the  objectives,  and  to 
get  rid  of  this  is  indeed  "  a  consummation  devoutly  to 
be  wished." 

Having  had  the  little  Histological  in  constant  use — 
i.  e.,  from  six  to  ten  hours  daily  —  I  arn  now  prepared, 
from  my  own  experience,  to  state  that  I  am  quite  well 
satisfied  with  the  fine  adjustment  as  placed  by  the 


44  HOW   TO    SEE   WITH   THE    MICROSCOPE. 

maker.  It  would  probably  take  me  a  trifle  longer  to 
adjust  nicely  an  objective  on  the  Histological,  and  but  a 
trifle ;  while,  on  the  other  hand,  all  the  objections  con- 
nected with  the  adjustment  at  the  nose-piece  are 
avoided. 

The  Histological,  as  furnished  by  the  maker,  has 
simply  a  plain  stage  with  spring-clips.  This  defect  did 
not  pass  unnoticed  by  the  writer,  Mr.  Zentmayer  re- 
sponding promptly  to  his  request  with  the  improvised 
stage  described  on  a  preceding  page. 

It  remains  to  be  noticed  that  the  Histological  has 
neither  rack  nor  pinion,*  and  that  the  coarse  adjustment 
is  effected  by  sliding  the  body  within  an  adjustable 
"  jacket."  There  is  no  novelty  in  this,  for  the  sliding 
tube  is  "as  old  as  the  hills,"  and  has  been  extensively 
adopted  in  the  construction  of  cheap  stands. 

The  author  felt  very  much  like  kicking  at  this  feature 
of  the  Histological.  In  a  little  time,  however,  experi- 
ence taught  him  that  the  sacrifice  of  the  rack  and  pinion 
was  not  such  a  serious  matter  as  might  be  supposed. 
The  sliding  movement  of  the  body  tube  within  its 
jacket  in  the  little  stand  is  very  smooth,  regular,  and 
reliable,  while,  on  the  other  hand,  there  are  some  ad- 
vantages accruing  to  the  slide  that  are  not  to  be  ob- 
tained by  the  use  of  the  rack  and  pinion. 

For  example:  suppose  we  are  working  ovsr  wet 
preparations,  and  unfortunately  the  front  of  the  objec- 
tive becomes  immersed  in  the  liquid — a  misfortune 

*Mr.  Zentmayer  now  furnishes  the  Histological,  with   or  without  the 
rack  and  pinion  coarse  adjustment. — AUTHOR. 


THE    AMERICAN   H1STOLOGICAL    STAND.  45 

liable  to  occur  daily.  It  is  then,  in  such  cases,  a  posi- 
tive convenience  to  be  able  to  pull  the  body-tube  out  of 
the  jacket,  cleanse  the  objective,  and  return  to  its  place. 
All  this  can  be  done  in  much  less  time  than  would  be 
required,  Avere  the  instrument  furnished  with  rack  and 
pinion,  to  unscrew  the  lens,  cleanse,  and  screw  in  place 
again. 

The  greatest  objection  that  the  writer  has  to  urge 
against  the  Histological  stand  is  this:  When  it  is 
placed  in  a  vertical  position,  there  is  a  liability  of  its 
tipping  forward.  This  can  be  prevented  by  clamping 
the  instrument  to  the  table  with  a  small  iron  clamp, 
such  as  are  used  by  carriage-builders  and  are  sold  at 
the  hardware  shops  for  a  dime.  In  this  simple  way  the 
stand  is  rendered  as  solid,  more  stable  indeed  than  those 
of  the  heaviest  build. 

One  of  my  correspondents,  to  whom  I  had  stated  the 
above-mentioned  objection,  informs  me  that  Mr.  Zent- 
mayer  has  made  some  changes  in  the  foot,  securing 
thereby  greater  steadiness. 

Previous  to  the  introduction  of  the  Histological,  it 
was  generally  taken  and  accepted  that  the  purchaser  of 
a  cheap  stand  ought  not,  in  the  nature  of  things,  to 
expect  an  instrument  capable  of  all  work.  To  a  slight 
extent,  and  to  a  slight  extent  only,  does  the  remark  hold 
good  to-day,  for  the  Histological  has  not  the  revolving 
platform,  for  the  measurement  of  angular  apertures 
(apertures  can,  however,  be  measured  on  the  stand), 
nor  has  it  the  circular  graduated  stage ;  nevertheless, 
the  Histological  will  accomplish  a  larger  variety  of 


46  HOW   TO   SEE   WITH   THE   MICROSCOPE. 

work  than  can  be  performed  on  the  "  Grand  American 
Stand  "  of  the  same  maker,  and  this,  too,  be  the  char- 
acter of  the  work  what  it  may,  be  it  the  study  of  a 
Histological  object  or  the  display  of  the  No.  20  of  the 
Moller  plate,  or  the  19th  band  of  Nobert. 

As  may  be  arrived  at  by  the  tenor  of  the  preceding- 
remarks,  the  author  regards  the  introduction  of  the 
histological  as  marking  an  era  in  the  progress  of  micro- 
scope stands.  The  long-sought  problem  has  been  solved, 
and  in  the  Histological  we  have  a  cheap,  reliable,  and 
universal  stand,  suitable  for  almost  any  work  which 
may  be  required,  and  capable  of  carrying  any  and  all  of 
the  various  accessories  which  in  the  past  have  been  sup- 
posed to  pertain  only  to  the  heavier  and  (so-called) 
first-class  instruments. 

Furthermore,  the  author  desires  in  this  place  to  put 
on  record  his  unfaltering  opinion  that,  in  the  devising, 
construction,  and  introduction  of  the  Histological  stand, 
the  maker  has  bestowed  a  greater  boon  on  the  "  body 
corporate  "  of  microscopists  than  has  been  accomplished 
by  others,  either  at  home  or  abroad.  If  there  be  an 
error  in  this  statement,  "  time,  with  its  revenges,  will 
set  it  forth." 


47 


TOLLES*   LARGE    "BB"   MICROSCOPE. 

This  instrument  was  designed  to  meet  the  require- 
ments of  the  scientific  investigator.     The  instrument, 


constructed  on  the  Jackson  model,  is  eighteen  inches 
high,  when  placed  in  a  vertical  position,  and  weighs 
about  fourteen  pounds.  The  curved  arm  is  supported 
on  a  steel  trunnion  between  two  strong  brass  pillars 


48  HOW  TO   SEE   WITH   THE   MICROSCOPE. 

made  for  durability,  and  not  liable  to  get  out  of  order, 
and  is  provided  with  means  ot  compensation  for  wear. 

It  has  rack  and  pinion  for  coarse  and  micrometer 
screw  for  fine  adjustment,  the  latter  being  placed  in 
front  of  the  body,  as  has  been  usual  in  first-class  instru- 
ments, on  the  Jackson  model.  It  is  furnished  with 
graduated  draw-tube ;  sub-stage  with  rack  and  pinion, 
and  centring  screws  for  accessory  apparatus ;  plane  and 
concave  mirrors  on  double-jointed  arm;  Tolles'  thin 
stage,  admitting  light  of  great  obliquity;  with  rectan- 
gular movements  by  screw  and  rack  and  pinion,  and 
rotation  on  the  optical  axis  of  about  270°. 

Mr.  Tolles  makes  a  modification  of  this  sized  stand, 
the  stage  being  carried  by  friction  rollers,  and  having 
entire  rotation  on  the  optical  axis.  The  cost  of  the  in- 
strument is  thereby  somewhat  enhanced. 

TOLLES'  LARGEST  "A"  MICROSCOPE 

weighs  twenty  pounds,  and  is  one  of  the  largest  and 
most  solid  instruments  extant.  The  stage  is  six  inches 
in  diameter,  and  makes  a  complete  revolution  on  the 
optical  axis.  The  whole  instrument  rotates  on  a  stout 
plate  graduated  to  degrees,  and  is  similar  in  all  respects 
of  style  and  construction  to  the  "  B"  stand. 

Either  of  the  two  stands  named,  made  by  Mr.  Tolles, 
may  be  unhesitatingly  pronounced  first-class.  The  work- 
manship is  of  the  very  highest  order ;  the  circular  stage 
can  be  so  nicely  adjusted  as  to  allow  of  an  entire  revo- 
lution, under  a  one-twenty-fifth  objective,  without  the 


TOLLE'S  STUDENT'S  MICROSCOPE. 


49 


object  being  sensibly  displaced.  Either  form  of  stand 
can  be  fitted  with  radial  arm  to  carry  accessory  appar- 
atus at  any  angle.  Any  thing  that  Mr.  Tolles  makes 
is  sure  to  be  made  well. 


TOLLES'  STUDENT'S  MICROSCOPE. 

This  stand  is  fifteen  inches  high,  weight  six  pounds; 
the  base,  uprights,  and  curved  arm  are  of  iron,  hand- 


somely japanned.  On  a  trunnion  joint,  made  on  a  plan 
to  wear  well,  the  instrument  can  be  placed  in  any  posi- 
tion, from  vertical  to  horizontal,  and  has  a  stop  to  pre- 
vent movement  in  either  direction  beyond  these  points. 
The  stage  is  plain,  with  spring-clips  for  holding  the  ob- 


50  HOW   TO   SEE   WITH   THE   MICROSCOPE. 

ject  slides ;  revolving-  diaphragm ;  concave  mirror,  with 
movement  to  give  oblique  light,  and  for  the  illumina- 
tion of  opaque  objects  the  mirror  is  removed  to  an  up- 
right stand.  The  coarse  adjustment  for  focus  is  effected 
by  sliding  the  compound  body  which  is  held  in  its  place 
by  a  spring;  fine  adjustment  by  a  movable  plate  and 
screw  on  the  stage,  which  is  efficient  with  high  powers. 
The  stand  is  made  with  all  the  care  bestowed  on  his 
first-class  instruments.  The  form  is  that  of  the  Jackson 
pattern.  To  this  instrument  Mr.  Tolles  supplies  several 
variations  and  additions,  as  a  matter  of  course  increas- 
ing the  cost  as  well  as  its  capacity.  Among  these  sev- 
eral extras  may  be  mentioned  sliding  stage,  giving  ver- 
tical and  horizontal  motions  by  hand,  and  adapted  to 
the  use  of  the  "  Maltwood  Finder;"  sub-stage  for  acces- 
sory apparatus ;  fine  adjustment  by  lever  and  microm- 
eter screw ;  rack  and  pinion  for  coarse  adjustment ;  thin 
glass  stage  to  rotate  on  the  optical  axis ;  the  stand  en- 
tirely of  brass,  etc.  For  a  "  student's  stand  "  this  is  an 
instrument  of  good  round  proportions.  It  stands  firmly 
on  its  legs,  and  the  stage  is  remarkably  roomy.  The 
body-tube  is  nickel-plated,  and  the  entire  instrument 
symmetrical  in  its  proportions,  and  not  without  pre- 
tensions to  style.  Like  all  of  Mr.  Tolles'  work,  it  is 
made  "  for  keeps."  There  are  many  of  them  in  use  and 
doubtless  giving  satisfaction. 

The  Bausch  &  Lomb  Optical  Company  manufacture 
several  excellent  stands,  which  were  designed  under  the 
immediate  superintendence  of  Mr.  Earnest  Gundlach. 
The  firm  furnish  some  seven  or  eight  models,  trom 
which  we  select  the  following  three : 


THE   PKOFESSIONAL   MICROSCOPE.  53 


THE  PROFESSIONAL   MICROSCOPE. 

This  is  the  largest  and  most  expensive  instrument 
made  by  the  company,  and  may  be  described  as  follows  : 
Heavy  brass  foot  and  pillars,  both  highly  finished, 
carrying  the  axis  for  inclination  of  the  body,  which 
movement  can  be  easily  tightened  or  loosened  by  two 
strong  milled-head  screws.  Coarse  adjustment  by  rack 
and  pinion,  moving  along  prismatic  slide,  of  first-class 
workmanship,  attached  to  the  body;  fine  adjustment  by 
a  new  and  patented  frictionless  motion.  The  object 
slide  rests  upon  a  newly  devised  carrier;  the  body  tube 
has  an  inner  draw  tube,  with  society  screw  to  which  ob- 
jectives of  very  long  focal  distance  can  be  attached ;  large 
plane  and  concave  mirrors ;  sub-stage  for  receiving  acces- 
sories of  standard  size,  and  two  revolving  diaphragms, 
one  of  the  latter  belonging  to  the  condenser ;  all  attached 
to  the  swinging  mirror  bar,  the  axis  of  which  is  placed  on 
the  level  of  the  object  so  that  the  diaphragm  and  mirror 
swing  concentrically  around  it.  The  mirror  as  well  as  the 
sub-stage  can  be  moved  on  the  iniiror-bar  to  and  from 
the  object,  and  both  can  be  removed,  the  latter  by  a  hor- 
izontal prismatic  slide.  The  sub-stage  ring  is  provided 
with  internal  "  society  screw"  for  objectives,  condenser, 
etc.  There  are  also  two  slot  diaphragms  of  different 
widths,  covering  the  whole  surface  of  the  mirror,  and 
only  allowing  light  to  pass  through  the  slot  in  such  a 
direction  that  very  sharp  shadows  by  oblique  light  will 
be  produced. 


56  HOW  TO   SEE   WITH  THE   MICROSCOPE. 


LARGE  STUDENT'S  MICROSCOPE. 

Heavy  japanned  cast-iron  foot,  with  highly  finished 
brass  pillars,  carrying-  the  axis  for  inclination  of  the 
body ;  brass  arm ;  coarse  adjustment  by  rack  and  pinion ; 
fine  adjustment  by  a  new  and  patented  motion.  The 
special  advantages  claimed  for  this  new  adjustment  are : 
(1)  exceedingly  easy  and  smooth  movement  ot  the  fine 
screw  both  ways;  (2)  perfect  freedom  from  all  lost 
motion;  (3)  perfect  freedom  from  any  side  motion  of 
the  image ;  and  (4)  extraordinary  durability. 

The  microscope  is  provided  with  a  movable  slide 
holder,  serving  as  a  substitute  for  a  mechanical  stage. 
This  slide  holder  consists  of  a  German-silver  plate  of 
very  light  weight,  moving  on  a  strong  glass  plate  which 
forms  the  immovable  stage;  only  four  small  points  of 
the  German-silver  plate  touch  the  top  of  this  glass 
stage,  while  two  prolongations  of  the  former,  bent 
downward  and  backward,  and  acting  as  springs,  press 
against  the  underside  of  the  glass  plate  with  just  suffi- 
cient force  to  keep  the  slide  holder  in  position,  and  to 
prevent  it  from  slipping  off  when  the  instrument  is 
inclined.  Two  small  knobs  facilitate  the  handling  of 
this  slide  holder,  and  it  is  claimed  that  this  arrange- 
ment exceeds  in  smoothness  and  evenness  of  motion  the 
movable  glass  stages  commonly  used,  while  the  mova- 
ble part  has  less  weight,  and  allows  the  glass  plate  to  be 
of  sufficient  strength  to  guard  against  easy  breaking. 

The  instrument  has  also  plane  and  concave  mirrors ; 
sub-stage  of  the  extra  size  required  to  receive  standard 


FAMILY   MICROSCOPE.  57 

sized  English  accessories;  revolving  diaphragms,  etc. 
These  are  all  attached  to  the  swinging  mirror  bar,  the 
axis  of  which  is  placed  at  the  level  of  the  object,  so  that 
the  diaphragm  and  mirror  swing  concentrically  around 
the  object.  The  mirror  can  also  be  moved  on  the  mir- 
ror bar  to  and  from  the  object,  and  the  distance  between 
the  latter  and  the  sub-stage  can  be  varied  by  reversing 
it.  Both  sub-stage  and  mirror  can  also  be  removed. 

It  is  to  be  observed  that  in  these  two  instruments  the 
importance  of  the  swinging  bar,  before  described  in 
connection  with  the  Centennial  and  Histological  stands 
of  Mr.  Zentmayer,  has  been  recognized  by  Mr.  Gund- 
lach.  The  mechanism,  however,  by  which  these  makers 
accomplish  the  swing  in  the  plane  ot  the  object,  is  by 
no  means  the  same  in  their  respective  stands.  Thus  the 
peculiar  method  of  securing  the  stage  to  the  limb,  em- 
ployed by  Mr.  Zentmayer,  allows  that  the  sub-stage 
with  its  accessories,  and  the  mirror,  be  brought  entirely 
above  the  stage,  the  only  thing  preventing  a,  full  revo- 
lution being  the  body  tube,  while  in  the  instruments  of 
Mr.  Gundlach  the  swinging-bar  plays  in  a  slot  cut  in 
the  rear  of  the  main  stage  plate,  and  the  swinging 
motion  is  thus  circumscribed  by  the  stage  slot. 

FAMILY  MICROSCOPE. 

This  has  japanned  cast-iron  foot  and  pillars  support- 
ing the  axis  which  carries  the  body,  so  that  it  may  be 
inclined  to  any  angle  revolving  diaphragm  below  the 
stage;  rack  and  pinion  for  adjustment  of  focus;  con- 


58 


HOW   TO   SEE   WITH   THE    MICROSCOPE. 


cave  mirror,  adjustable  for  oblique  light;   plain  stage 
with  spring  clips. 


This,  although  the  least  expensive  instrument  made 
by  Mr.  Ghmdlach,  is  nevertheless  well  put  together, 
strong  and  really  serviceable,  and,  with  proper  care, 
ought  to  last  a  lifetime.  It  can  be  readily  made  capa- 

NOTE.— Since  the  above  was  written,  we  learn  that  Mr.  Gundlach  has 
separated  from  the  B.  &  L.  optical  company,  and  that  he  now  devotes  his 
entire  attention  to  the  manufacture  of  object  glasses,  the  Messrs.  Bausch 
&  Lomb,  however,  continued  to  furnish  both  stands  and  objectives,  and  are 
by  purchase,  the  proprietors  of  many  of  Mr.  Gundlach's  patents. 


BULLOCH'S  FIRST-CLASS  MICROSCOPE  A  1.         59 

ble  of  doing  most  ot  the  work  required  by  the  physician 
and  to  those  who  can  afford  the  luxury  of  having  two 
stands  something  of  this  kind  will  be  found  a  real  con- 
venience. 

Mr.  W.  H.  Bulloch,  of  Chicago,  manufactures  seven 
different  forms  of  stands,  from  which  we  present  the 
following : 


BULLOCH'S  FIRST-CLASS  MICROSCOPE  A  1. 

It  has  the  concentric,  rotating,  and  mechanical  stage, 
with  graduations  for  measuring  angles ;  is  also  adjusta- 
ble, so  that  it  can  be  accurately  and  perfectly  centered. 
There  are  also  graduations  connected  with  the  horizon- 
tal and  vertical  movements  of  the  stage,  by  wyhich  the 
exact  position  of  an  object  can  be  noted  and  found  with 
more  certainty  than  with  the  "  Maltwood  Finder." 
The  whole  stage  is  sufficiently  thin  to  admit  an  angle 
of  oblique  light  as  high  as  134  degrees,  and,  if  required, 
the  stage  can  be  made  reversible. 

The  sub-stage  is  fitted  with  the  most  complete  move- 
ments for  centring  or  for  oblique  light  with  the  achro- 
matic condenser.  It  has  one-fourth  inch  movement 
each  way ;  rack  and  pinion ;  divided  circle  for  polariz- 
ing; is  so  arranged  that  the  sub-stage  can  be  used 
either  above  or  below  the  main  stage,  and  can  be  oper- 
ated by  hand  or  by  tangent  screws ;  it  is  entirely  separ- 
ate from  the  mirror,  but  if  desired  can  quickly  be 
connected,  so  that  the  mirror  and  sub-stage  turn 


60  HOW  TO   SEE   WITH   THE   MICROSCOPE. 

together  around  the  same  centre,  which  is  the  thickness 
of  an  average  slide  over  the  stage. 

The  entire  sub-stage  with  its  milled  heads  can  be 
taken  off,  so  that  there  shall  be  nothing  in  the  way 
when  using  direct  light.  The  mirror  is  arranged  so 
that  it  can  be  used  in  any  direction,  backward,  forward, 
over  or  under  the  stage.  The  mirror  and  also  the  sub- 
stage  have  graduated  circles,  so  that  the  obliquity  can 
be  noted. 

The  movement  of  the  body  is  effected  by  rack  and 
pinion  connected  with  two  milled  hea^s,  which  connect 
with  the  lever  of  the  slow  motion,  thus  preserving  the 
distance  between  the  objective  and  the  eye-piece.  The 
slide  on  the  body  tube  is  long  and  broad,  thus  prevent- 
ing vibration  or  lateral  motion  when  using  the  milled 
heads  or  the  micrometer  screw ;  the  latter  is  grooved 
so  that  it  can  be  used  for  photographic  purposes. 

The  instrument  is  mounted  on  tripod  base,  with  re- 
volving platform.  The  platform  is  graduated,  and  upon 
it  two  standards  are  fixed,  between  which  the  instru- 
ment turns  to  the  angle  when  so  used,  or  turning  hori- 
zontally for  drawing,  or  for  measuring  angular  aperture. 
The  centre  on  which  the  instrument  turns,  when  placed 
horizontally,  is  in  a  direct  line  with  the  object  on  the 
stage. 

The  binocular  model  is  arranged  with  rack  and  pinion 
for  different  width  of  eyes ;  the  prism  is  so  fixed  that 
the  distance  remains  the  same.  The  society  screw  at 
the  end  of  the  body  is  arranged  as  a  safety  nose-piece, 
with  spring,  so  that  the  danger  of  breaking  slides  is 


BULLOCH'S  FIRST-CLASS  MICROSCOPE  A  1.         63 


avoided.  The  iris  diaphragm  has  the  society  screw  so 
that  any  objective  can  be  used  for  a  condenser,  or  it 
can  be  used  above  the  objective  as  an  adapter,  to  reduce 
the  light  in  the  instrument.  The  stand  is  nineteen 
inches  high  when  arranged  for  use. 

This  stand  and  the  "  Centennial "  of  Mr.  Zentmayer, 
may  be  considered  as  rival  instruments,  and  neither  of 
them  enters  the  list  for  a  slow  race ;  both  are  respec- 
tively the  masterpieces  of  their  makers,  and  are  claimed 
to  be  the  very  embodiment  of  all  and  singular  that  can 
be  desired  by  the  microscopist. 

Purely  in  the  interest  of  the  reader,  we  proceed  to 
compare  these  stands  with  each  other ;  the  final  verdict 
shall  be  left  a  matter  of  individual  election. 

First.  The  price  of  both  instruments  is  precisely  the 
same,  while  the  Bulloch  has  additional  the  iris  dia- 
phragm, the  mechanical  stage  with  its  adaptations  for 


64  HOW   TO   SEE   WITH  THE   MICROSCOPE. 

use  as  an  object  finder,  the  safety  nose-piece,  the  duplex 
arrangement  of  sub-stage  and  mirror  arm,  whereby 
these  move  in  unison,  or  independently  of  each  other, 
and  the  centring  and  rotating  sub-stage. 

To  meet  this,  it  might  be  claimed,  on  the  part  of  the 
Centennial,  that  the  above-named  additional  contri- 
vances have  been  purposely  discarded  by  the  maker  of 
the  Centennial ;  that  really  there  is  no  particular  advan- 
tages to  be  derived  from  the  iris  diaphragm,  the  mechan- 
ical stage,  the  centring  sub-stage,  or  the  duplex 
arrangement  above  referred  to,  and  that  all  these  con- 
trivances serve  unduly  to  complicate  the  instrument. 

As  to  the  centring  sub-stage,  it  might  be  also  said 
that  with  the  introduction  of  the  "  swing"  there  is  no- 
longer  need  of  wide-angled  achromatic  condensers. 
Furthermore  the  secondary  body  of  the  Centennial 
being  itself  accurately  centred,  there  is  no  occasion  to- 
introduce  especial  appliances  for  this  purpose. 

It  will  be  noticed  that  in  the  Centennial  the  mirror 
and  sub-stage  rise  without  hindrance  above  the  stage, 
the  movement  being  only  stopped  by  contact  with  the 
body  tube  (supposing  the  smaller  stage  to  be  employed,) 
all  this  time  the  mirror  remaining  in  fixed  focal  posi- 
tion. To  accomplish  the  rise  of  the  mirror  above  the 
stage  in  Mr.  Bulloch's  stand,  the  jointed  arms  connected 
with  the  mirror  are  brought  into  play,  and  indeed  can- 
not be  dispensed  with.  A  close  comparison  of  the 
mechanism  will  reveal  the  fact  that  in  respect  to  the 
swinging  arrangement,  there  is  a  wide  difference  in 
the  construction  of  the  two  instruments.  The  angle  of 


MR.  BULLOCK'S  "D"  STAND.  67 

obliquity  obtained  with  the  Centennial  stage,  is  greater 
than  that  obtainable  in  Mr.  Bulloch's  stand. 

The  principal  points  are  thus  presented ;  it  remains 
for  the  reader  to  use  his  own  election.  Either  of  the 
two  stands  will  bear  comparison  with  any  foreign  stand 
extant. 

Mr.  Bulloch  also  supplies  another  stand,  which  he 
calls  his 

SMALL  BEST  STAND  "  A-B." 

This  instrument  is  similar  in  construction  to  the 
large  stand,  but  smaller,  excepting  the  body  tube, 
which  is  of  the  standard  length  in  all  his  instruments. 

ME.  BULLOCH'S  "D"  STAND. 

This  has  been  selected  by  the  author  for  description 
principally  because  it  is  a  medium-sized  "  student's 
stand,"  and  furnished  with  a  concentric  adjustable  stage, 
it  being  desirable  to  present  as  much  variety  as  possible 
within  our  circumscribed  limits. 

The  adjustable  concentric  stage  can  be  centred  to  any 
objective ;  the  edge  of  stage  is  bevelled  and  graduated, 
so  that  angles  of  crystals  can  be  measured ;  it  has  a 
complete  revolution.  Its  glass  stage  is  perforated  in 
the  centre,  has  brass  fittings,  so  that  the  "Maltwood 
Finder  "  can  be  used ;  and  its  motion  is  perfectly  smooth 
under  the  highest  power.  To  the  underside  of  stage  is 
fitted  a  tube  for  accessories;  this  can  be  removed  so 
that  the  utmost  angle  of  oblique  light  can  be  obtained. 
Plane  and  concave  mirrors  and  lateral  motion  for  ob- 


68  HOW   TO   SEE   WITH   THE   MICROSCOPE. 

lique  light,  coarse  adjustment  by  rack  and  pinion,  fine 
ditto,  by  delicate  screw,  diaphragm;  draw  tube  gradu- 
ated, with  society  screw  at  end.  The  instrument  can 
be  inclined  to  any  angle,  has  English  horseshoe  base, 
and  is  sixteen  inches  high  when  arranged  for  use. 

BULLOCK'S  NEW  BIOLOGICAL  STAND. 

The  cut  shows  the  instrument  about  two-fifths  the 
real  size,  it  stands  twelve  and  a  half  inches  high,  and 
the  stage  three  and  a  half  from  the  table  when  in  an 
upright  position.  Body  tube  five  inches  long,  draw 
tube  five  inches  long;  with  marked  ring  when  drawn 
to  the  standard  length.  Standard  size  and  sub-stage 
fitting,  adapted  in  sub-stage  with  the  society  screw  for 
the  use  of  objectives  as  condenser,  and  the  diaphragm 
fits  in  the  same  screw  and  can  be  used  close  up  to  the 
object  slide.  Plain  and  concave  mirrors  each  swing 
over  the  stage  can  be  used  together,  or  separate,  can 
be  clamped  in  any  position,  by  milled  screws  shown 
behind  the  limb.  Spring  stop  to  mirror  and  sub-stage 
when  in  line  axis.  Concentric  revolving  stage,  can 
be  adjusted  concentric  to  the  axis  by  means  of  capstan- 
head  screws,  the  sub-stage  also  can  be  adjusted  con- 
centric by  means  of  capstan  screws.  Spring  clips  to 
stage  or  the  sliding  glass  stage  as  desired. 

When  the  stage  is  not  required  to  revolve,  it  can  be 
clamped  in  any  position  by  the  milled  screw  shown  in 
front;  and  when  there  is  any  danger  of  injuring  the 
stage  by  the  use  of  acids,  the  stage  lifts  out  of  the  ring 
in  which  it  revolves,  and  any"  ordinary  piece  of  glass 


E.  &  J.  BECK'S  MICROSCOPES.  71 

can  be  used  on  the  ring  by  placing  the  instrument  in  an 
upright  position.  Back  and  pinion  quick  motion,  lever 
fine  motion  placed  behind  the  limb  moving  the  whole 
body  tube;  the  body  tule  is  fitted  with  broad  gua^e 
screw  one  and  a  quarter  inch  diameter,  and  in  which 
fits  adapted  with  regular  society  screw,  tripod  base 
with  single  pillar,  the  axis  on  which  the  instrument 
turns  is  placed  in  such  position  that  the  instrument  is 
perfectly  balanced  when  placed  in  horizontal  position 
for  drawing.  When  so  placed  the  centre  of  eye-piece 
is  seven  and  a  half  inches  from  table,  the  standard  is 
furnished  with  a  B  eye-piece.  The  mirror  and  sub- 
stage  can  be  fitted  with  divided  arch  for  measuring  the 
obliquity  of  light,  the  sta^e  can  also  have  divided  circle 
for  measuring  the  angle  of  crystals.  Stand  all  made  of 
polished  brass. 

E.  &  J.  BECK'S  MICROSCOPE. 

E.  &  J.  Beck,  of  London,  the  old  and  well-known 
firm,  have  established  an  American  agency  in  the 
United  States.  In  their  facilities  for  the  production  of 
first-class  workmanship  they  are  not  excelled.  As 
makers  of  London  instruments,  they  have  been  long 
and  favorably  known,  and  the  Londoner  points  with 
commendable  pride  to  the  names  of  Ross,  Powel,  Lea- 
land,  and  E.  &  J.  Beck. 

No  attempt  can  be  made  in  these  pages  to  describe  a 
tenth  part  of  the  stands  manufactured  by  the  Messrs. 
Beck.  Their  catalogue  will  be  found  to  include  all  the 
various  grades,  where  may  be  found  elegant  and  expen- 


72  HOW  TO   SEE   WITH   THE   MICROSCOPE. 

sive  stands,  which,  with  the  accompanying  accessories, 
etc.,  cost  $1,600  and  upwards,  down  to  the  more  simple 
forms,  within  the  reach  of  all.  It  is  from  the  latter 
that  we  make  the  following  selections : 

BECK'S  POPULAR  MICROSCOPE,  MONOCULAR  OR  BINOC- 
ULAR. 

In  this  stand  the  arrangement  for  changing  the  angle 
of  inclination  of  the  body  is  new  and  durable.  It  has 
coarse  adjustment  by  rack  and  pinion,  fine  adjustment 
by  micrometer  screw ;  the  stage  is  fitted  with  improved 
object-holder  and  concentric  revolving  fittings;  the 
mirror  slides  on  the  main  stem,  and  has  its  own  semi- 
circle for  universal  motions.  A  diaphragm  is  provided 
with  perforated  revolving  disk.  The  instrument  is  on 
the  "transverse  arm"  model,  which  has  been  so  ex- 
tensively used  by  Koss,  of  London,  as  well  as  others. 

The  instrument  can  be  furnished  with  all  the  usual 
accessory  apparatus  as  supplied  by  the  makers;  a 
mechanical  stage,  giving  horizontal  and  vertical  motions 
by  screws,  is  also  furnished  if  desired. 

BECK'S  ECONOMIC  MICROSCOPE. 

The  makers  say  in  their  catalogue  that  "  the  micro- 
scope is  now  such  an  absolute  necessity  for  the  student, 
to  enable  him  satisfactorily  to  carry  on  his  investiga- 
tion, that  it  is  more  than  ever  incumbent  on  the  optician 
to  construct  a  sound  economic  instrument  adapted  to 
the  special  requirements  of  this  large  and  increasing 
class." 

To  this  proposition  let  this  little  book  say,  Amen. 


FLGJL 


BECK'S  ECONOMIC  MICROSCOPE.  77 

"  For  ordinary  pathological,  physiological,  and  botan- 
ical investigations,  many  of  the  delicate  adjuncts  applied 
to  the  higher-priced  instruments  are  unnecessary,  and 
tend  rather  to  contuse  than  to  assist  the  beginner." 

To  this  let  these  pages  say  again,  Amen. 

"  A  firm  stand  and  well-corrected  object-glasses  are, 
however,  indispensable." 

In  response  to  this  we  not  only  say  amen,  but  shall, 
in  the  proper  place,  have  something  further  to  add. 

"The  stand  of  the  "Economic"  is  made  in  two 
forms:  the  one  with  a  sliding  adjustment  for  focussing 
the  object,  and  the  other  where  the  quick  movement  is 
produced  by  rack  and  pinion.  On  both  stands  the  fine 
adjustment  is  given  by  means  of  a  milled  head  at  the 
top  of  the  stem.  The  stand  is  fitted  with  the  society 
screw. 

The  foundation  of  the  stand  is  a  heavy  horseshoe 
base  A,  at  the  head  of  which  is  a  firm  pillar  B,  having 
at  its  top  a  hinge  joint  C,  which  allows  the  body  D  to 
be  inclined  to  any  angle,  and  is  sufficiently  firm  to  per- 
mit of  its  beins:  placed  horizontal  for  use  with  the 
camera  lucida. 

The  body  tube  is  short,  but  by  means  of  the  length- 
ening draw  tube  V  can  be  made  of  the  standard  length. 

In  the  more  expensive  stand  the  coarse  adjustment  is 
by  rack  and  pinion;  in  the  cheaper  instruments  the 
quick  movement  is  produced  by  sliding  the  body  D  up 
and  down  the  tube  H,  sliding  over  the  inner  stem  with 
a  spring  inside,  the  fine  adjustment  being  accomplished 
by  the  milled  head  I. 


78  HOW   TO   SEE    WITH   THE   MICROSCOPE. 

The  stage  K,  upon  which  the  object  is  placed,  has 
two  springs  LL,  the  pins  attached  to  which  may  be  in- 
serted in  any  ot  the  four  holes  on  the  stage,  and  by 
their  pressure,  which  can  be  varied,  they  will  hold  the 
object  under  them,  or  allow  it  to  be  moved  about  with 
the  greatest  accuracy. 

The  mirror  M,  besides  swinging  in  the  rotating  semi- 
circle N,  attached  to  a  bar  O,  with  a  joint  at  each  end, 
allowing  a  lateral  movement,  so  as  to  throw  oblique 
light  on  the  object,  and  for  this  purpose  the  tube 
beneath  the  stage,  carrying  the  diaphragms,  has  semi- 
circular openings  cut  on  either  side,  leaving  a  clear  and 
thin  stage,  allowing  the  utmost  obliquity  of  illumina- 
tion. This  tube  also  carries  the  polariscope,  etc. 

The  diaphragm  P  slides  in  the  sub-stage  fitting,  and 
consists  of  a  tube  containirg  two  caps  furnishing  two 
sizes  of  openings,  immediately  in  contact  with  the 
under  surface  of  the  slide  to  be  examined,  and  also 
completely  cutting  off  all  light  from  the  mirror,  when 
opaque  objects  are  to  be  viewed. 

The  instrument  packs,  without  being  taken  to  pieces, 
in  a  small  and  neat  case,  is  very  convenient  for  travel- 
ing purposes,  and  entirely  adequate  for  very  many  pur- 
poses. The  general  workmanship  seems  in  keeping 
with  the  reputation  of  its  makers,  while  its  cost  places 
it  within  the  reach  of  all.  At  an  advanced  cost,  it  can 
be  supplied  with  all  the  usual  accessories. 

Last,  but  not  least,  I  now  have  the  pleasure  of  pre- 
senting to  my  readers 


BECK'S  NEW  HISTOLOGICAL  DISSECTING  MICROSCOPE.  79 


BECK  S  NEW  HISTOLOGICAL  DISSECTING  MICROSCOPE. 

This   instrument   combines  a  compound  microscope 
with  a  single  and  dissecting  one  in  a  very  compact  and 


practical  form.  The  stout  immovable  arm  carrying  the 
lens  when  used  as  a  single  microscope,  is  so  arranged 
that  a  compound  body  with  eye-piece  and  draw  tube  may 
be  attached  to  its  upper  surface,  whilst  beneath  it  is 


80  HOW  TO   SEE   WITH   THE   MICROSCOPE. 

fitted  with  the  society  screw,  whereby  an  objective 
may  be  used  with  it.  The  rack-and-piuion  adjustment 
work  so  smoothly  that  a  one-fourth  inch  objective  may 
be  focussed  with  exactness.  The  mirror  beneath  the 
stage  is  so  adjusted  upon  a  swinging  arm  that  it  may 
be  turned  up  over  the  stage  for  the  illumination  of  an 
opaque  object.  A  revolving  diaphragm,  with  various 
sized  openings,  is  attached  to  the  under  side  of  the 
stage.  The  outfit  consists  of  a  single  lens  of  one-inch 
focus  for  dissecting  and  botanical  work,  and  an  achro- 
matic objective  of  one-fourth  inch  focus,  the  same  as 
furnished  with  the  economic  microscopes,  and  one  eye- 
piece, giving  a  range  of  powers,  with  the  draw  tube, 
of  between  200  and  300  diameters,  a  pair  of  brass  pliers, 
two  dissecting  needles  in  ebony  handles  and  a  glasa 
plate  with  ledge.  The  whole  packed  in  a  neat  mahog- 
any case  with  lock.  Several  accessories  are  applicable 
to  this  instrument. 

THE   NEW    NATIONAL    MICROSCOPE. 

The  stand  which  is  fifteen  inches  in  height,  is  con- 
structed entirely  of  brass,  of  the  highest  finish  and  best 
workmanship,  having  a  broad,  heavy  tripod  base.  From 
the  centre  of  this  base  rises  a  stout  column,  to  the  top 
of  which  is  attached,  by  a  firm  joint,  the  Jackson  model 
arm,  carrying  the  compound  body,  by  which  the  inclin- 
ation can  be  varied  to  any  degree,  from  vertical  to  hori- 
zontal, the  whole  instrument  being  perfectly  steady  and 
free  from  tremor  in  any  position.  The  very  highest 
powers  may  be  used  with  it,  as  the  body,  being  sup- 


THE   NEW   NATIONAL   MICROSCOPE.  83 

ported  by  the  arm  throughout  its  entire  length,  cannot 
have  any  unsteadiness  or  motion  of  its  own. 

The  quick  adjustment  of  focus  is  effected  by  means  of 
rack  and  pinion,  with  large  milled  heads,  which  works 
so  smoothly  that  there  is  no  need  to  use  the  fine  adjust- 
ment for  any  power  lower  than  one-quarter  of  an  inch. 
The  latter  adjustment  is  by  means  of  a  delicate  micro- 
meter screw  and  lever  attachment,  working  with  abso- 
lute freedom  from  all  motion,  and  by  which  the  very 
highest  powers  may  be  focused  with  the  greatest  exact- 
ness. 

The  stage  is  of  glass,  with  a  complete  rotation  in  the 
optic  axis,  upon  the  top  of  which  is  a  sliding  object- 
holder,  very  thin,  and  with  a  spring  clip  for  holding  the 
object  in  place  during  rotation.  This  clip  is  removable, 
in  an  instant,  and  the  stage  forceps  can  be  inserted  in  its 
place,  thus  allowing  the  latter  to  be  moved  about  with 
the  object-carrier.  Beneath  the  stage  is  a  tube  carrying 
all  the  sub-stage  apparatus,  as  the  achromatic  conden- 
ser, Wenham's  parabola,  polarizing  apparatus,  etc.,  etc. 
This  is  securely  attached  to  the  stage  by  a  bayonet- 
catch,  and  can  be  instantly  detached,  leaving  a  very 
thin  and  unobstructed  stage  for  oblique  illumination. 
The  shutter  diaphragm  is  of  novel  construction,  with  the 
various-sized  openings  almost  in  contact  with  the 
underside  of  the  object  under  examination,  a  great 
improvement  upon  the  old  revolving  disk  diaphragm. 
A  double  mirror  concave  and  plane  is  hung  upon  a 
swinging  bar,  and  with  every  possible  motion  for  di- 
rect and  oblique  illumination. 


84  HOW  TO   SEE   WITH  THE    MICROSCOPE. 


THE   NEW  ACME   STAND. 


During  the  session  of  the  "  congress"  of  microscop- 
ists  at  Indianapolis  in  1878,  Mr.  John  W.  Sidle,  of 
Philadelphia,  and  myself  formed  ourselves  into  a  com- 
mittee of  two  for  the  purpose  of  devising  a  new  micro- 
scope stand. 

Mr.  Sidle  and  myself  were  agreed  in  our  opinions 
that  notwithstanding  the  recent  improvements  which 
of  late  years  had  obtained,  that  there  was  still  room 
for  further  effort  in  the  construction  of  microscopes. 

Ip  was  then  and  there  proposed,  deliberated  on,  and 
agreed,  that  we  would  unite  our  energies  in  the  en- 
deavor to  construct  a  microscope  stand,  which  should 
combine  every  possible  good,  be  equal  to  any  and  all 
work,  exhibiting  all  the  latest  appliances,  and  withal, 
to  combine  really  reliable  workmanship,  at  the  lowest 
possible  cost,  in  fact  at  figures  no  higher  than  those 
commanded  by  inferior  instruments. 

This  arrangement  contemplated  that  the  author 
should  furnish  all  the  suggestions  which  his  long  ex- 
perience with  the  microscope  might  afford,  while  Mr. 
Sidle  was  charged  with  the  mechanical  part  in  the  con- 
struction of  the  new  stand. 

This  agreement  has  been  carried  out  to  the  letter, 
and  from  the  date  named,  until  August  last,  Mr.  Sidle 
and  myself  have  been  in  close  correspondence,  and  for 
the  purpose  named. 

The  first  stand  built  under  our  compact  was  received 
by  me  from  Mr.  Sidle  early  in  August  last,  and  as  a 


THE   NEW  ACME   STAND.  85 

matter  of  course,  it  got  a  pretty  severe  overhauling-, 
suffice  it  to  say  that  I  became  so  much  pleased  with  our 
new  bantem,  that  I  gave  it  the  name  it  bears,  and  have 
no  hesitancy  in  recommending  this  joint  production  of 
Mr.  Sidle  and  myself  to  my  friends. 

With  this  preliminary  statement,  I  proceed  to  give 
the  reader  a  brief  description  of  our  new  stand. 

The  Acme  with  closed  tube,  when  in  the  vertical  posi- 
tion, is  about  fourteen  inches  in  heighth,  and  its  weight 
about  five  pounds. 

The  foot  is  of  cast-iron;  "horseshoe"  shaped  and 
similar  to  the  Hartnack  patterns,  combining  in  the 
smallest  compass  the  necessary  weight  and  accompany- 
ing solidity.  For  real  work  in  the  laboratory  this  form 
of  foot  is  believed  to  be  superior  to  all  others.  For 
those  who  prefer  the  tripod  model,  Mr.  Sidle  will  fur- 
nish this  form  at  the  same  cost,  or  in  finished  brass  at 
an  additional  cost  of  $3.50. 

The  entire  instrument  is  supported  by  a  heavy  single 
pillar  of  solid  brass,  the  lower  portion  of  which  passes 
through  the  cast-iron  foot,  the  two  parts  being  held 
firmly  together  by  a  clamp-screw  underneath  the  foot. 
By  virtue  of  this  arrangement,  the  foot  can  be  detached 
almost  instantly,  or,  by  a  half-turn  of  the  lower  clamp, 
the  foot  can  be  reversed  on  the  axis  of  the  pillar,  thus 
ensuring  the  greatest  stability  when  the  stand  is  in  the 
horizontal  position.  The  lower  shoulder  of  the  brass 
pillar  passing  through  the  foot  is  accurately  turned  and 
fitted,  and  when  desired  the  moulding  at  the  part  of 
the  brass  pillar  immediately  adjacent  to  the  top  of  the 


86  HOW   TO   SEE   WITH   THE   MICROSCOPE. 

foot  can  be  divided  to  degrees  for  the  measurement  of 
angular  aperture,  my  own  stand  is  thus  arranged. 

Besides  those  already  mentioned  other  advantages 
occur,  from  having  the  foot  of  the  stand  removable, 
some  of  which  may  be  enumerated  as  follows: 

First,  by  detaching  the  base,  the  instrument  can 
easily  be  carried  in  the  pocket ;  it  is  also  much  easier  to 
pack,  and  occupies  much  less  space  in  the  packing.  It 
can  thus  be  carried  from  place  to  place  even  in  the  nar- 
row accommodations  afforded  by  a  small  valise,  the 
bother  of  lugging  about  the  usual  microscope  case 
being  no  longer  necessary. 

Second,  Mr.  Sidle  provides  at  a  small  extra  cost  a 
neat  black  walnut  base  board,  furnished  with  small 
lamp  fitted  with  universal  movements.  This  board  has 
also  the  necessary  brass  fittings  to  receive  the  pillar  of 
the  microscope,  which  can  be  clamped  to  the  board. 
By  this  arrangement  all  that  is  necessary  to  convert  the 
instrument  into  a  first-class  hand  microscope  is  to  bring 
the  body  to  the  horizontal  position  and  to  adjust  the 
object  and  the  illumination. 

With  the  stand  as  thus  arranged  I  have  repeatedly 
exhibited  objects  illustrative  of  my  lectures  to  the  col- 
lege class  of  150  students,  the  instrument  being  passed 
from  hand  to  hand  throughout  the  entire  class,  and  re- 
turned to  me  everything  remaining  in  perfect  order. 

To  teachers  this  feature  of  the  stand  will  be  of  value. 
It  will  also  be  found  a  great  convenience  at  times  when 
the  microscope  is  called  on  to  furmsh  entertainment  in 


THE   NEW   ACME   STAND.  87 

the  family  circle,  and  objects  can  thus  be  exhibited 
with  great  rapidity. 

By  means  of  a  strong  trunnion  joint  the  body  of  the 
instrument  can  be  inclined  at  any  desired  position 
between  the  vertical  and  horizontal,  the  requisite 
stability  of  motion  being  secured  by  heavy  "cheek- 
blocks;"  the  joint  has  also  compensation  for  wear. 

All  the  working  part  of  the  Acme  above  the  base  are 
of  solid  brass,  bright  finished,  and  nicely  lacquered. 

The  main  body-tube  is  one  and  five-sixteenth  inches 
in  diameter.  This  tube  articulates  with  the  limb  by 
means  of  heavy  "  T"  guides  or  angle  pieces,  thus  secur- 
ing broad  bearing  surfaces  and  also  perfect  freedom 
from  lateral  displacement.  Mr.  Sidle  has  put  himself 
to  much  trouble  to  perfect  this  portion  of  the  stand. 

The  main-tube  is  five  inches  in  length.  This  is  sup- 
plemented with  a  draw-tube,  which  can  be  drawn  out 
to  the  standard  length  of  ten  inches  when  desired. 

The  coarse  adjustment  is  by  rack  and  pinion.  The 
rack  is  well  cut  and  durable,,  and  the  movement  of  the 
tube  by  means  of  operating  the  large  milled  heads  is 
exceedingly  smooth  and  entirely  without  "lost  motion." 

The  fine  adjustment  is  by  a  large  milled  head  place 
at  the  rear  of  the  limb,  and  operating  the  main  tube. 
This  milled  head  is  one  and  one-fourth  inches  in  diam- 
eter, and  is  divided  into  twenty  divisions.  It  acts 
directly,  i.  e.9  without  lever,  on  a  micrometer  screw 
cut  fifty  threads  to  the  inch,  each  division  of  the  milled 
head  representing  one  one-thousandth  of  an  inch.  The 
fine  adjustment  can  therefore  be  easily  made  to  answer 


88  HOW   TO   SEE   WITH  THE   MICROSCOPE. 

the  purpose  of  a  micrometer  for  measuring-  small  inter- 
vals, or  for  the  measurement  of  cover  glasses,  etc.  In 
this  adjustment  the  same  security  against  lateral  dis- 
placement is  provided  for  by  means  of  the  "  T"  angle- 
pieces,  as  applied  to  the  rack  and  pinion  movement. 

The  lower  end  of  main  tube  carries  a  nose-piece  fitted 
with  the  "  society  screw."  This  piece  can,  however,  be 
detached  so  that  the  broad-guage  objectives  now  in  pro- 
cess of  construction  can  be  used  on  this  instrument. 

The  main  stage  consists  of  a  circular  metal  plate, 
three  and  one-quarter  inches  in  diameter,  firmly  bolted 
to  the  heel  of  the  limb,  and  in  such  a  manner  as  to  be 
isolated  from  the  movements  of  the  sub-stage  apparatus; 
four  holes  are  drilled  through  the  main  stage  plate, 
and  so  arranged  that  the  spring-  clips  may  be  adjusted 
to  hold  the  object-slide  in  either  a  vertical  or  horizon- 
tal position.  The  spring  clips  may  also  be  tiansferred 
to  the  under  surface  of  the  stage,  holding  the  object- 
slide  in  contact  therewith,  when  very  oblique  illumina- 
tion is  to  be  employed.  The  well-hole  is  of  the  usual 
size  and  is  provided  with  a  standard  screw-thread,  by 
means  of  which  the  Woodward  prism  and  other  acces- 
sory pieces  can  be  readily  placed  in  position.  The  stand 
is  thus  fitted  for  such  emergencies  as  required  a  fixed 
and  central  sub-stage,  separate  from  the  movements  of 
the  mirror ;  the  polariscope  is  also  nicely  provided  for. 

(NOTE.— It  has  lately  come  to  the  surface  that  the  diameter  of  the 
*•  society  screw  "  is  not  sufficiently  large  to  meet  the  requirements  of  the 
optician  when  low  powers  of  the  widest  apertures  are  demanded.  Mr. 
Sidle  is  now  making  for  the  author  a  one -inch  glass  having  a  diameter  of 
over  one  inch,  and  the  Acme  has  been  designed  to  meet  such  requirements). 


THE   NEW   ACME    STAND.  89 

The  main  stage  has  also  conveniences  for  centering. 
Furthermore,  a  solid  plug  is  furnished  which  screws 
into  the  well-hole,  and  forming  when  desired,  a  solid 
stage.  This  plug  has  an  "X"  engraved  thereon  for 
centering  purposes. 

The  sub-stage  proper,  as  well  as  the  concave  mirror, 
are  attached  to  a  swinging  bar  by  dove-tailed  blocks, 
The  slides  having  compensation  for  wear,  the  sub-stage 
can  be  centered.  It  is  one  and  one-half  inches  in  diam- 
eter and  is  fitted  to  carry  any  of  the  accessory  pieces 
usually  accompanying  a  first-class  outfit.  The  sub- 
stage  and  the  mirror  both  slide  with  easy  friction  on 
the  swinging  bar. 

The  swing-bar  traverses  the  face  of  a  circle  of  brass 
placed  at  the  rear  of  the  stage,  the  centre  of  this  circle 
being  in  the  plane  of  an  object  placed  on  the  stage; 
the  centre  of  this  circular  plate  is  solid,  that  is  to  say, 
it  presents  a  solid  core  of  about  one  inch  diameter; 
outside  of  this  an  angular  groove  is  cut  therein,  in  which 
.swings  the  heel  of  the  swing  bar,  the  method  of  at- 
tachment of  the  swing  bar  to  the  circular  plate  giving 
great  solidity  as  well  as  firmness  in  motion.  Thus  it 
will  be  seen  that  the  "  swinger"  swings  not  on  a  centre 
but  around  a  centre.  This  part  of  the  mechanism  needs 
only  to  be  seen  to  be  appreciated. 

The  mirror  is  of  course  removable,  and  a  toy  candle- 
holder  is  provided  to  take  its  place  for  the  measure- 
ment of  apertures. 

A  supplemental  circular  and  revolving  stage  plate  is 
.also  furnished,  which  "slips"  on  and  off  instantly  as 


90  HOW  TO   SEE   WITH  THE   MICROSCOPE. 

may  be  required.  And  by  virtue  of  a  nice  little  con- 
trivance of  Mr.  Sidle's,  the  rotatory  movement  is  very 
smooth  and  nearly  as  central  as  would  be  expected  from 
stands  of  much  higher  cost. 

When  desired,  Messrs.  Sidle  and  Poulk  furnish  a 
mechanical  stage  which  slips  on  and  off  in  place  of  the 
rotary  plate  above  mentioned;  this  mechanical  stage 
has  vertical  or  horizontal  motions  to  the  extent  ot 
three-fourths  of  an  inch.  This,  however,  involves  an 
extra  cost  of  $14. 

To  exhaust  the  list  of  American  makers  would  be 
quite  beyond  the  province  of  this  book.  There  remain 
the  names  of  Grrunow,  McAllister,  Pike,  Queen, Schrauer, 
Wales,  George  Wale,  and  others.  Descriptions  of  the 
stands  supplied  by  these  various  makers  have  been 
omitted,  partially  because  the  author  unfortunately  has 
little  acquaintance  with  their  work,  while  that  of  oth- 
ers which  at  times  he  has  seen,  seem  practically  to  be 
much  the  same  as  those  already  described,  and  the 
reader  would  gain  nothing  by  the  repetition. 

By  way  of  concluding  this  chapter,  and  as  supple- 
mental to  what  has  already  been  said  as  to  the  choice  of 
a  stand,  the  writer  would  especially  insist  on  the  im- 
portance of  a  stage  thin  enough  to  admit  a  beam  of 
light  at  70°,  from  axis,  not  that  the  observer  will 
always  work  with  oblique  light,  but,  when  occasion  calls 
fcr  it,  the  stand  should  be  capable  of  responding,  and, 
as  has  been  before  hinted,  in  these  latter  days  these 
kind  of  calls  occur  more  frequently  than  was  the  case  in 
the  days  of  yore.  Let  the  novice  especially,  then,  who 


THE   NEW   ACME    STAND.  91 

proposes  to  purchase  a  stand  that  he  will  not  feel  com- 
pelled to  sell  again  in  a  few  years,  in  order  to  procure 
a  better  one;  keep  this  point  well  in  mind. 

The  author,  too,  unhesitatingly  gives  his  support  to- 
those  stands  having  the  swing  stage  and  mirror;  the 
advantages  accruing  from  this  late  improvement  are 
very  valuable,  of  which  we  make  particular  mention  of 
one,  to  wit: 

In  former  times,  when  sub-stages  were  practically  a 
fixture,  it  became  necessary,  in  order  to  secure  oblique 
light,  to  employ  acchromatic  condensers  of  wide  aper- 
tures and  short  focal  distance ;  the  instrument  was  costly,, 
and  necessitated  the  employment  of  accurate  and  expen- 
sive sub-stage  fittings,  and,  in  general,  could  only  be  em- 
ployed at  a  great  sacrifice  of  pains,  time  and  attention. 
With  the  introduction  of  the  swinging  sub-stage  and 
mirror,  all  this  is  a  thing  of  the  past;  the  wide-angled 
condenser  is  no  longer  necessary  for  the  display  of  diffi- 
cult structures;  on  the  other  hand,  it  now  seems  desir- 
able to  employ  condensers  of  the  lowest  angles,  the 
required  obliquity  being  obtained  by  swinging  the  sub- 
stage,  mirror  and  condensers  to  the  proper  angle.  The 
expensive  centring  apparatus  not  being  required  with 
the  low-angled  condenser,  their  cost  and  bother  are  thus 
avoided ;  at  the  same  time  better  results  are  obtained, 
and  in  a  simpler  and  more  convenient  way. 

There  are  other  advantages,  too,  pertaining  to  the 
use  of  the  swinging  stage  and  mirror,  of  which  mention 
will  be  made  in  the  succeeding  pages. 

Finally,  let  me  impress  on   the  mind  of  the  readef 


92  HOW   TO   SEE   WITH   THE   MICROSCOPE. 

that  the  large  and  expensive  stands  are  not  at  all  neces- 
sary; the  smaller  and  cheaper  stands,  if  due  care  be 
taken  in  the  selection,  will  do  any — practically  all  work 
required  in  the  progress  of  scientific  investigation. 
Furthermore,  keep  constantly  in  mind  the  fact  that  a 
great  deal  of  work,  legitimately  in  the  line  of  investi- 
gation, can  only  be  conveniently  accomplished  with  the 
small  stands. 

Where  expense  is  no  object,  or  even  when  one  can 
afford  two  stands  without  feeling  thus  crippled  in  other 
directions,  it  will  be  found  a  luxury  to  have  the  two. 
In  the  very  nature  of  things,  it  is  impossible  to  obtain 
the  firmness  and  solidity  of  a  large  and  heavy  instru- 
ment through  the  medium  of  the  smaller  stands,  and 
occasionally  this  stability  is  a  real  convenience,  resulting 
in  a  saving  of  time  and  labor,  as,  for  instance,  in  draw- 
ing with  the  camera  lucida.  The  graduated  revolving 
platform  for  the  measurement  of  angles  of  aperture, 
tmd  similarly  the  circular  graduated  stage,  with  its 
•centring  adjustments,  are  handy  things  to  have  in  the 
house,  but  cost  money,  and,  as  a  rule,  can  be  dispensed 
with. 

And  last — in  this  matter,  far  from  being  least — should 
the  res  angusta  domi  pinch  so  bitterly  as  to  compel  you 
for  the  time  being  to  omit  some  necessary  investment, 
then  I  say,  by  all  means  make  sure  of  the  necessary  ob- 
ject glasses,  quantity  and  quality  included,  and  let  the 
stand  " sweat"  until  the  "good  time  coming"  shall 
enable  you  to  provide  a  new  and  superior  instrument. 
Remember,  too,  that  the  finest  and  most  expensive 
stand  extant,  fitted  to  a  poor  objective,  becomes  not 
only  a  dangerous  tool,  but  also  a  positive  nuisance. 


CHAPTER  II. 

WHAT  IS  ANGULAR  APERTURE. 

During  the  lengthy  controversy  which  occured  be- 
tween Mr.  F.  A.  Wenham.  optician  to  the  firm  of  Ross 
and  Co.,  of  London,  and  Mr.  R.  B.  Tolles,  of  Boston, 
Mass.,  the  originator  of  the  celebrated  duplex  object 
glasses,  the  former  presented  ideas  as  to  the  functions 
and  nature  of  angular  aperture  which  were  not  in  strict 
accordance  with  the  popular  views.  Since  then  others 
have  done  likewise,  and  it  may  be  well  enough  to  leave 
the  question  open,  without  attempting  to  answer  the 
above  interrogatory  at  all. 

For  the  information  of  those,  however,  who  are  just 
entering  the  study  of  microscopy,  Ave  will  undertake  ta 
tell  what  angular  aperture  was,  or  to  be  more  definite, 
what  it  was  in  1856 ;  and  for  this  purpose,  the  author 
selects  the  definition  found  in  the  Micrographic  Diction- 
ary by  Messrs.  Griffith  and  Henfrey,  a  work  generally 
acknowledged  as  authority  in  matters  microscopical. 

The  angular  aperture  of  an  object-glass  is  the  angle 
measured  by  the  arc  of  a  circle,  the  centre  of  which  is 
formed  by  the  focal  point  of  the  object-glass,  the  radii 
being  formed  by  the  most  extreme  lateral  rays  which 
the  object-glass  will  admit. 

Thus  let  L,  in  the  left-hand  figure  1  below,  repre- 
sent the  lower  portion  of  a  microscope,  objective, — 


94  HOW  TO    SEE   WITH   THE   MICROSCOPE. 

a,  perpendicular  section  of  the  lowest  combination  of  an 
object  glass  of  small  aperture. 

"a  is  the  angle  of  aperture,  and  f  e the  most  oblique 
rays  which  the  object-glass  will  admit.  The  angle  is 
measured  by  the  dotted  arc  b  in  the  object-glass  of 


larger  aperture  (Fig.  to  the  right) ;  the  arc  6,  which 
measures  the  angle,  is  much  larger,  and  the  radii  repre- 
senting the  extreme  lateral  rays  are  much  more  oblique. 
Hence  it  is  evident  that  the  object-glass  of  larger  aper- 
ture admits  all  those  rays  admitted  by  that  of  less 
aperture,  and  a  certain  number  of  other  rays,  these 
being  more  oblique." 

The  above  definition  has  been  and  is  now  generally 
accepted.  Messrs.  Griffiths  &  Henfrey  proceed  to  give 
their  demonstrations  of  the  effect  of  aperture,  as  thus 
defined,  in  an  interesting  and  lengthy  article,  one  that 
is  well  worth  perusal  by  those  desiring  to  know  how 
things  stood  twenty-two  years  ago.  Our  limited  space 
forbids  its  reproduction  here. 


HOW  SHALL  WE  MEASURE  ANGULAR  APERTURE.   95 


HOW  SHALL  WE  MEASURE  ANGULAR  APERTURE. 

While  the  nature  and  functions  of  angular  aperture 
remain  a  matter  of  controversy,  this  too  may  be  allowed 
to  remain  an  open  question.  Kecognizing,  however, 
the  fact  that  object-glasses  continue  to  be  made  and 
sold,  the  makers  claiming  for  them  specific  apertures, 
we  proceed  to  give  the  plan  usually  adopted  by  the 
optician,  and  at  the  same  time  adapted  to  the  use  of 
those  working  with  the  smaller  class  of  stands. 

It  will  be  advantageous  to  the  beginner  to  operate 
either  in  a  dark  room  or  in  the  evening.  Select  a  good 
sized  table,  and  on  this,  at  the  end  nearest  the  operator, 
pin  down  a  large  sheet  of  paper,  say  twenty  inches 
square.  On  this  paper  place  the  microscope,  bring  the 
tube  to  a  horizontal  position, -and  screw  on  the  object- 
ive to  be  tested.  Mark  with  a  pencil  certain  points 
along  the  base  of  the  stand,  so  as  to  enable  you  to 
describe  a  circle  with  pencil  and  dividers,  in  which  the 
base  will  just  revolve  without  lateral  play.  Next, 
provide  a  common  candle,  and,  if  necessary,  cut  this 
down  so  that  the  height  of  the  flame  shall  be  level  with 
the  objective  in  its  horizontal  position ;  light  the  candle, 
point  the  objective  directly  at  the  light,  having  pre- 
viously removed  all  sub-stage  incumbrances,  crouching 
down,  and  with  the  eye  at  the  eye-piece,  adjust  the 
direction  of  the  instrument  as  nearly  as  possible  to  the 
candle ;  the  field  of  view  will  of  course  be  illuminated 
from  the  radiant. 

Now  revolve  the  entire  instrument,  being  careful  to 


96  HOW   TO    SEE    WITH    THE    MICROSCOPE. 

keep  the  base  always  within  the  circle  drawn  on  the 
paper,  and  continue  the  movement  (either  to  the  right 
or  left,  as  the  case  may  be),  until  one-half  of  the  field 
shall  be  bisected — i.  e.,  one-half  bright  and  one-half  in 
the  shade.  Now  select  some  straight  portion  of  the 
base,  marking  a  straight  line  coincident  therewith  with 
a  pencil,  or,  placing  a  rule  in  contact  with  any  two- 
salient  angles  of  the  base,  draw  a  line. 

Next,  revolve  the  entire  stand  in  the  contrary  direc- 
tion, passing  the  candle,  and  until  you  again  get  a  field 
half  bisected  similarly,  as  before  mentioned.  Now 
selecting  the  same  side,  or  the  same  two  salient  corners 
of  the  stand,  mark  another  line. 

These  two  lines  will  be  found  divergent  with  each 
other,  and  with  a  parallel  rule  it  will  be  found  easy  to 
produce  parallel  lines  which  can  be  continued  until 
they  meet;  this  done,  it  only  remains  to  measure  the 
angle  obtained  with  a  common  protractor,  or  other  in- 
strument designed  for  the  measurement  of  angles. 

Where  tolerable  accuracy  is  important  it  will  be  well 
to  cross-question  the  result  by  repeating  the  operation. 
There  ought  not  to  be  a  discrepancy  of  more  than  one- 
half  of  one  degree. 

Those  who  possess  the  large  stands  fitted  with  gradu- 
ated and  revolving  platform  will  of  course  avail  them- 
selves of  the  convenience ;  the  operation  is  practically 
the  same;  thus,  having  bisected  the 'field  (say  to  the 
right),  read  the  angle,  which  will  be  indicated  by  a 
mark  on  the  platform  adjacent  to  the  graduations ;  then 
bisect  the  field  to  the  left,  read  the  angle  again,  sub- 


OBJECT   GLASSES.  97 

tract  one  reading-  from  the  other,  and  the  difference  is 
the  angle  of  aperture. 

There  being  no  means  for  the  actual  determination  of 
the  bisection  of  the  fields,  this  having  to  be  judged  of 
by  estimation,  follows  that  the  plan  is  not  rigidly 
accurate ;  the  author  has,  however,  measured  repeatedly 
the  same  object-glass,  following  as  above  described,  and 
without  a  variation  in  the  results  of  more  than  a  half 
degree;  many  of  his  pupils,  too,  on  their  very  first 
attempts,  are  quite  as  successful. 

The  bisection  of  the  fields  is  much  more  easily  arrived 
at  in  the  evening. 

OBJECT-GLASSES. 

Years  ago  wrote  Dr.  Carpenter  thus: 

"It  may  be  safely  affirmed  that  the  most  perfect 
object-glass  is  that  which  combines  all  the  preceding 
attributes  (viz.,  defining  power,  penetrating  power,  or 
focal  depth,  resolving  power,  and  flatness  of  field)  in 
the  highest  degree  in  which  they  are  compatible  one 
with  another.  But,  as  has  just  been  shown,  two  of  the 
most  important — viz.,  penetrating  power,  and  resolv- 
ing power — stand  in  such  opposite  relations  to  the 
angular  aperture,  that  the  highest  degree  of  which  each 
is  in  itself  capable  can  only  be  obtained  by  some  sacrifice 
of  the  other ;  and  therefore  cf  two  objectives  which  are 
respectively  characterized  by  the  predominance  of  those 
opposite  qualities,  one  or  the  other  will  be  preferred  by 
the  microscopist,  according  to  the  particular  class  of 
researches  he  may  be  carrying  on ;  just  as  a  man  who  is 

7  Microscopy. 


98  HOW   TO   SEE    WITH   THE    MICROSCOPE. 

about  to  purchase  a  horse  will  be  guided  in  his  choice 
by  the  kind  of  work  for  which  he  destines  the  animal. 
Hence  it  shows,  in  the  author's  estimation,  just  as 
limited  an  appreciation  of  the  practical  applications  of 
the  instrument,  to  estimate  the  merits  of  an  object- 
glass  by  its  capability  of  showing  certain  lined  or  dotted 
tests,  without  any  reference  to  its  penetrating  power  or 
defining  power,  as  it  would  be  to  estimate  the  merits  of 
a  horse  merely  by  the  number  of  seconds  within  which 
he  could  run  a  mile,  or  by  the  number  of  pounds  he 
could  draw;  without  any  reference,  in  the  first  case, 
either  to  the  weight  he  could  carry,  or  the  length  of 
time  during  which  he  could  maintain  his  speed,  and,  in 
the  second  case,  either  to  the  rate  of  his  draught  or  his 
power  of  continuing  the  exertion.  The  greatest  capac- 
ity for  speed  alone,  the  power  of  sustaining  it  not  being 
required,  and  burden  being  reduced  almost  to  nothing, 
is  that  which  is  sought  in  the  racer;  the  greatest 
power  of  steady  draught,  the  rate  of  movement  being  of 
comparatively  little  importance,  is  that  which  is  most 
valued  in  the  cart-horse;  but  for  the  ordinary  carriage- 
horse  or  roadster,  the  highest  merit  lies  in  such  a  combi- 
nation of  speed  and  power  with  endurance  as  cannot 
coexist  with  the  greatest  perfection  in  either  of  the  first 
two.  The  author  feels  it  the  more  important  that  he 
should  express  himself  clearly  and  strongly  on  this  sub- 
ject, as  there  is  a  great  tendency  at  present,  both  among 
amateur  microscopists  and  among  opticians,  to  look  at 
the  attainment  of  that  resolving  power  which  is  given 
by  angular  aperture  as  the  one  thing  needful.  .  .  . 


OBJECT   GLASSES.  99 

It  is  neither  the  only  nor  yet  the  chief  work  of  the 
microscope  (as  some  appear  to  suppose)  to  resolve  the 
markings  of  the  siliceous  valves  of  the  diatomacea ;  in 
fact  the  interest  which  attaches  to  observations  of  this 
classier  se,  is  of  an  extremely  limited  range.  .  .  . 
And  the  more  carefully  we  look  into  the  history  of 
those  contributions  to  our  knowledge  which  have  done 
the  most  to  establish  the  value  of  the  microscope  as  an 
instrument  of  scientific  research,  the  more  clear  does  it 
become  that  for  almost  every  purpose  except  the  resolu- 
tion,of  the  diatom  tests,  objectives  of  moderate  angular 
aperture  are  to  be  decidedly  preferred."  * 

This  quotation — essentially  true  when  first  published 
— has  been,  and  to  a  considerable  extent  now  is,  the 
orthodox  faith  ot  the  microscopist.  It  has  been  en- 
dorsed by  everybody,  both  at  home  and  abroad;  the 
world  of  observers  have  rested  peacefully  at  ease  on  its 
broad  platform;  the  man  of  science  was  serene  and 
content  with  his  medium  apertures;  but  it  was  the 
crowning  glory  of  the  quack  that  a  "  good  honest," 
low-angled,  "working"  triplet  cost  only  a  dollar  or 
two.  Ajid  it  was  a  fact,  that  so  far  as  faith  was  con- 
cerned, the  scientist  and  the  veriest  quack  were  in  the 
same  boat  together,  and  both  found  pleasure  in  endors- 
ing the  teachings  of  Dr.  Carpenter. 

It  seems  to  me  that  this  singular  state  of  things  can 
be  easily  accounted  for.  The  hard-working  investiga- 
tors had  little  opportunity  to  study  object-glasses,  their 
time  being  completely  occupied,  and  their  eyes  sorely 

*"The  Microscope  and  It,  Revelations"  fifth  edition,  1875,  page  204. 


100  HOW   TO   SEE    WITH   THE   MICROSCOPE. 

taxed  in  the  daily  routine  of  labor  and  study.  Their 
glasses  were  the  best  that  could  be  procured  when  pur- 
chased, and,  as  far  as  their  personal  experience  with 
them  could  attest,  their  experience  was  in  harmony 
with  the  laws  laid  down  by  Dr.  Carpenter ;  and  they 
had  "  no  time  to  waste  "  in  fussing  over  "  diatom  tests," 
etc. 

On  the  other  hand,  the  empiric  replies,  "  Your  high- 
angled  glasses  are  all  well  enough  for  the  diatom  man, 
but  for  my  work  give  me  reliable  French  triplets  of 
moderate  apertures;"  and  in  this  statement  the  author 
is  in  entire  and  perfect  harmony ! 

The  author  repeats,  that  ten  years  ago  the  doctrines 
taught,  as  contained  in  the  previous  quotation  of  Dr. 
Carpenter,  were  essentially  true;  he  has  no  fault  to 
find  with  their  original  publication,  but  he  does  regret 
that  Dr.  Carpenter  has  allowed  them  to  retain  their 
place,  unchanged  or  unrevised,  in  his  late  editions. 

Let  us  glance  for  a  moment  at  the  history  of  the  ob- 
ject-glass as  connected  with  its  aperture.  Years  since 
it  was  known  that  the  exhibition  of  surface-markings 
required  to  a  greater  or  leeser  extent  the  employment 
of  lateral  or  oblique  light;  width  of  aperture  hence 
became  a  desideratum,  at  least  in  such  glasses  as  were 
to  be  used  with  this  object  in  view. . 

Whether  right  or  wrong,  demands  were  made  on  the 
optician  for  objectives  possessing  increased  apertures. 
Notably,  this  demand  was  first  met  successfully  by  our 
own  countryman  ,  the  veteran  Charles  A.  Spencer,  who 
produced  a  glass  of  wider  angle  than  had  been  pre- 


OBJECT   GLASSES.  101 

viously  accomplished  and  thereby  astonishing  the  world, 
sorely  punching  the  English  opticians  (who  flattered 
themselves  on  secure  ground  at  the  head  of  the  profes- 
sion) with  an  exceedingly  sharp  stick;  with  this  glass 
Mr.  Spencer  succeeded  in  displaying  both  sets  of  lines 
on  the  diatom,  now  known  as  Navwula  Spencerii. 

The  London  makers  followed  suit,  giving  especial  at- 
tention to  the  extension  of  aperture,  and,  as  might  be 
reasonably  expected,  the  problem  was  to  get  light  of 
extreme  obliqaity  somehow  through  the  lens,  nor  were 
they  (the  makers)  very  particular  to  stand  on  the  order 
of  its  going;  hence  it  came  about  that  very  many 
glasses  were  made  and  sold  having  increased  angle,  by 
virtue  of  which  they  were  able  to  display  certain  ac- 
knowledged difficult  tests ;  but,  on  the  other  hand,  the 
lateral  pencils  being  poorly  corrected  (if  corrected  at 
all),  these  glasses  could  not  compete  by  centrally  dis- 
posed light  with  the  well-corrected  but  narrow  angles 
previously  in  use. 

It  was,  therefore,  to  the  wide-angled  glasses  of  that 
day  that  Dr.  Carpenter's  remarks  had  force,  the  highest 
possible  angle  attainable  being  then  limited  by  popular 
opinion  to  155°.  What  is  now  known  and  recognized 
as  a  high-angled  glass  of  175°  was  then  not  only 
unknown,  but  would  have  been  deemed  a  sheer  im- 
possibility, and  it  therefore  becomes  obvious  that  any 
remarks  at  the  time  referred  to,  whether  by  Dr.  Car- 
penter or  by  other  authors,  cannot  be  applied  consist- 
ently to  the  wide-angled  glasses  of  the  present  date. 

Those  were  the  days,  too,  when  the  resolution  of  the 


102  HOW   TO   SEE   WITH   THE    MICROSCOPE. 

nineteenth  band  of  the  Nobert  test-plate  was  said  "  to 
be  a  matter  of  faith  rather  than  of  sight."  The  curious 
reader  is  informed  that  the  original  of  the  quotation 
will  not  be  found  in  the  last  edition  of  the  ' l  Microscope 
and  its  Revelations ! " 

Again,  the  high-angled  objective,  as  at  present  con- 
structed, is  an  entirely  different  affair  from  that  of 
former  times.  In  place  of  achromatism,  then  thought 
to  be  the  ultima  thule  of  perfection,  the  finest  glasses 
now  made  can  hardly  be  said  to  be  achromatic.  And 
then,  again,  the  immersion  system  has  been  adopted 
with  its  manifold  advantages.  Improvement  upon  im- 
provement has  almost  marked  the  rolling  months  of 
the  calendar,  while  each  succeeding  year,  to  the  number 
of  ten  or  more,  has  been  richly  laden  with  the  fruits  of 
the  optician. 

In  this  wonderful  march  of  progress,  our  own  coun- 
try, I  am  proud  to  say,  has  ever  been  at  the  front,  and 
with  colors  flying.  As  before  stated,  Spencer,  with  his 
resolution  of  the  navicula,  commenced  this  march  of 
progress,  and  slackened  not  the  pace  until  the  reputa- 
tion of  American  objectives  were  duly  acknowledged 
abroad.  Then,  indeed,  he  retired  for  a  time,  resting 
gracefully  on  his  well- won  laurels;  and  now  appears 
Tolles  at  the  van,  who  with  almost  superhuman  genius 
and  energy  grapples  with  the  very  laws  of  optics,  and 
bends  them  to  his  inflexible  will ! 

Notwithstanding  that  the  reputation  of  the  country 
was  quite  safe  in  the  hands  of  Mr.  Tolles;  Spencer, 
after  a  year  or  two  of  rest,  again  comes  forward,  assisted 


OBJECT   GLASSES.  103 

by  his  two  sons,  both  of  them,  as  a  matter  of  course, 
N "  to  the  manner  born,"  and  in  the  very  prime  of  life 
and  activity. 

Thus  far  I  have  simply  referred  to  Spencer  and 
Tolles,  because  they  have  contributed  largely  to  the 
production  of  high-angled  objectives;  but  the  list  of 
American  opticians  is  not  thus  complete;  we  have 
Wales,  Zentmayer,  Grundlach,  and  Grunow  yet  in 
reserve,  whose  productions  in  their  several  lines  are 
not  inferior  to  any  imported. 

In  the  foregoing  brief  and  general  history  of  the 
American  wide-angled  objective,  the  conclusion  is  in- 
evitable, first,  that  during  the  past  ten  years  something 
has  been  accomplished,  and  that  in  the  interim  our 
opticians  have  not  been  idle ;  secondly,  that  the  modern 
high  angled  glass  is  to  be  judged  of  strict!}7  on  its  merits, 
and  not  by  what  was  affirmed  of  a  medium  aperture  ten 
long  years  ago. 

The  converse  of  this  is  equally  true,  and  the  author, 
in  presenting  his  views  of  to-day,  declines  to  be  held 
responsible  for  what  the  future  may  bring  forth. 

In  this  place  it  may  be  well  to  consider  what>  in 
common  parlance,  constitutes  a  high-angled  glass.  The 
writer  has  already  in  print  stated  his  individual  views 
which  have  since  undergone  no  change.  As  a  rule,  refer- 
ence being  made  to  wide  apertures,  most  persons  are 
prepared  for  some  great  show  of  figures,  such  as  "175°" 
or  "179°";  others  might  call  for  nearly  "180°";  and 
then  again,  others  there  are  who  would  insist  on  pass- 
ing the  "  impossible"  180°  corner,  and  revel  among  the 


104  HOW   TO    SEE    WITH   THE    MICROSCOPE. 

balsam  angles  to  the  tune  of  100°,  or  even  higher. 
In  dealing  with  objectives  of  short  focal  distance,  all 
this  may  be  well  enough;  the  writer,  however,  prefers 
to  regard  as  high-angled,  any,  and  all  glasses,  without 
reference  to  their  focal  lengths,  which  are  endowed 
with  the  widest  apertures  obtainable.  If  this  platform 
be  accepted,  then  it  will  occur  that  a  one-inch  of  50° 
should  be  classed  as  a  high-angled  objective,  and  simi- 
larly, a  two-inch  of  25°.  And,  again,  it  would  also  then 
occur  that  a  one-sixth  of  130°,  which  fifteen  years  ago 
ranked  as  a  wide,  would  now  be  classed  as  a  glass  of 
medium  aperture.  And  furthermore  it  may  possibly 
(yea probably}  have  place,  that  there  are  many  observers 
to-day,  loud  in  their  denunciations  of  the  "wide-angles," 
falling  back  on  "The  Microscope  and  its  Revelations" 
for  authority,  who,  in  their  habitual  use  of  what  are 
now  known  as  medium  apertures,  are  in  truth  the  real 
culprits,  to  whom  and  for  whom  were  Dr.  Carpenter's 
original  remarks  intended. 

As  has  been  suggested  on  a  previous  page,  there  may 
be  seriously  some  question,  not  only  as  to  angular  aper- 
ture per  se,  but  as  to  what  constitutes  the  measure  of 
the  same.  It  is  one  thing  to  get  light  through  an  ob- 
jective, and  quite  another  to  bring  said  light  into  the 
traces,  and  render  it  of  use  to  the  observer.  There  are, 
too,  scores  of  high-angled  glasses  (so-called)  sold  as 
having  angle  of  i?5°,  and  possibly  more,  that  are 
entirely  worthless  when  worked  with  pencils  beyond 
130° ;  indeed,  many  that  I  have  seen  would  utterly  fail 
when  compared  with  a  really  good  glass  of  115°. 


OBJECT    GLASSES.  105 

The  writer  has  before  him  a  glass  of  the  latter  angle, 
(115°,)  made  by  C.  A.  Spencer  &  Sons.  It  is  what 
they  call  one  of  their  "  professional  series" — a  dry  one- 
fourth  ;  the  makers  ought  not  to  expect  that  this  glass 
should  be  called  on  for  work  requiring  oblique  pencils 
greater  than  100°. 

Now  this  glass — this  professional  one-fourth — will 
give  me  real  good  shows,  even  when  worked  at  all  the 

53  o  7 

obliquity  obtainable  on  my  Zentmayer  stand ;  and  thus 
have  I  seen  with  it  the  longitudinal  markings  on  the 
balsamed  surriella  of  the*  Moller  test-plate,  and  this  is  a 
test  that  will  defeat  many  dry  eighths,  engraved  by 
their  makers  as  having  160°  or  more  angle. 

From  this  little  experiment — one  that  the  writer  has 
repeated  scores  of  times  in  the  interests  of  his  friends — 
some  curious  conclusions  might  be  arrived  at,  which, 
although  possibly  coherent  and  plausible  in  detail, 
become  absurd  when  considered  collectively;  thus  it 
might  be  held : 

First.  That  both  glasses  having  at  least  160°  of  aper- 
ture, are  in  fact  high-angled  glasses. 

Second.  That  of  the  two  named,  the  Spencer  is  the 
better  glass. 

Third.  That  the  Spencer  objective  has  really  but 
an  angle  of  115°,  as  marked  by  its  maker;  that  its  capa- 
bility of  admitting  working  beams  up  to  140°  gives  it 
no  real  claim  to  those  figures. 

Fourth.  That,  as  any  good  eighth  of  140°  will 
easily  show  the  longitudinal  markings  of  the  surriella, 
it  is  proven  that  the  one  referred  to  has  not  that  angle 


106  HOW   TO    SEE    WITH   THE   MICROSCOPE. 

at  all,  and  is,  in  fact,  but  a  medium  power  glass — the 
general  verdict  being  that  it  is  an  indifferent  one  at  the 
best. 

Fifth.  That  the  capacity  of  an  objective  to  display 
markings  on  balsamed  and  difficult  tests,  at  or  near  the 
limits  of  its  aperture,  is  no  index  of  angular  aperture. 
In  the  case  presented,  if  it  so  be  that  the  eighth,  when 
worked  at  140°,  gave  fair  and  distinct  images  of  the  sur- 
riella,  then  there  is  no  reason  to  dispute  the  angle  a& 
claimed  for  the  glass ;  let  the  experiment  be  repeated 
an  using  angle  of  120°,  and  over  dry  as  well  as  bal- 
samed mounts. 

The  above  may  be  taken  as  representing  individual 
differences  of  opinion.  Either  of  the  conclusions  pre- 
sented have  been  urged  on  our  attention  time  and  time 
again.  To  the  second,  third,  and  fourth,  the  author  gives 
his  assent,  and  has  never  allowed  an  opportunity  to  pass 
without  exposing  by  actual  demonstration  the  fallacy 
contained  in  the  fifth. 

From  the  preceding,  then,  it  becomes  apparent  that 
there  is  much  difference  of  opinion  as  to  what  consti- 
tutes angular  aperture  or  the  measurement  thereof. 
Until  there  can  be  some  more  precise  plan  arrived  at, 
let  the  purchaser  of  any  objective  imperatively  demand  : 

First.  That  the  objective,  in  general,  work  with  its 
full  vim  fully  up  to  the*  limits  of  the  aperture  claimed 
for  it;  that  the  images  be  strong,  vigorous,  brilliant, 
and  without  distortion,  and  that  such  images  shall  not 
be  surpassed  in  any  particular  by  any  similar  glass, 
without  reference  to  its  angle.  If  it  be  that  you  have 


OBJECT   GLASSES.  107 

a  wide  aperture  in  hand,  see  that  its  work  by  central  or 
centrally  disposed  light  is  not  excelled  by  any  objective 
of  narrow  angle  extant.  In  calling  on  the  glass  at  the 
limits  of  its  aperture,  demand,  and  see  to  it  particularly, 
that  there  be  no  letting  down  of  general  performance, 
that  the  images  remain  strong  and  vigorous,  that  the 
corrections  are  not  impaired,  and  even  with  the  widest 
apertured  objective  known,  that  there  be  no  sensible 
distortion  of  the  image. 

Again,  if  it  so  be  that  you  desire  thus  to  test  an  ob- 
jective claiming  considerable  aperture,  say  170°  or  175% 
and  adjustable,  note  whether  there  be  any  special  ad- 
justment required  when  worked  at  or  near  the  limits  of 
its  aperture,  other  than  necessary  for  its  correct  per- 
formance by  central  light;  if  this  be  found  the  case, 
the  indications  are  that  the  two  sets  of  pencils  are  not 
in  harmony  with  each  other — as  the  Germans  say,  are 
not  "married."  It  will  be  necessary  to  use  a  little 
discretion  here,  for  some  of  the  very  finest  glasses  re- 
quire a  slight  change  of  adjustment  under  the  condi- 
tions named.  The  less  of  this  especial  adjustment, 
however,  the  better. 

Any  objective  that  will  stand  acceptably  the  fore- 
going- tests  may  be  allowed  to  ' '  pass  muster  "  as  to  its 
aperture  sans  peur  et  sans  rejiroche. 

In  the  act  of  writing  the  above,  the  author  was  inter- 
rupted by  a  friend  with  the  remark,  "  Are  you  not 
screwing  things  down  pretty  fine?  Don't  you  see  that 
your  method  not  only  is  a  severe  test  as  to  working 


108  HOW   TO    SEE   WITH   THE   MICROSCOPE. 

-angle,  but  is  also  a  severe  test  as  to  the  general  quali- 
ties ot  an  objective?" 

In  response  to  this  interrogatory,  I  reply,  that  it's 
high  time  things  were  "screwed  down."  As  to  the 
latter  portion  of  the  remark  of  my  friend,  it  may  be 
observed  that  the  directions  given  indicate  a  part,  and 
part  only,  of  the  course  to  be  pursued  in  testing  the 
performance  of  a  really  first-class  American  objective 
of  wide  aperture. 

The  plan  proposed  is  liable  to  another,  and,  in  the 
minds  of  some,  a  most  serious  objection;  says  one, 
"  Don't  you  see  that  you  have  advanced  no  positive 
guage?  Your  idea  simply  is  to  compare  one  glass  with 
.another  —  in  short,  it  means  'fighting  objectives" 
Selah! 

SOMETHING  FURTHER   ABOUT   OBJECTIVES. 

There  is  another  matter  of  common  acceptance  which 
has  in  the  past  made  some  mischief;  I  refer  to  the  fact 
that  the  focal  or  working  distance  of  an  objective  has 
been  and  is  considered  the  index  of  its  capacity  for  cer- 
tain classes  of  work.  Thus,  the  incli  has  been  set  apart 
for  the  study  of  such  objects  as  required  examination, 
with  powers  from  50  to  150  diameters,  and  where  its 
comparatively  long  working  distance  was  desirable, 
while  the  one-fiftieth,  whose  lowest  power  of  2,500 
diameters  and  its  exceedingly  short  working  distance, 
<;ould  not  perform  the  work  of  the  inch  —  the  one- 
fiftieth  being  reserved  for  the  investigation  of  the  most 
minute  organisms,  and  under  the  highest  amplifications. 


SOMETHING   FURTHER   ABOUT    OBJECTIVES. 

Now,  in  the  instance  cited  the  popular  idea  is  correct. 
The  inch  cannot  do  the  work  of  the  fiftieth,  nor  can  the 
fiftieth  do  the  work  of  the  inch,  and  each,  as  to  the 
other,  are  to  be  appropriately  brought  into  use. 

But,  as  is  well-known,  between  and  intermediate  to 
the  scope  of  the  two  glasses  named,  there  are  several 
objectives  having  not  only  intermediate  but  variable 
focal  lengths.  Among  these  latter,  too,  are  to  be 
found  the  objectives  known  as  "  medium  powers,"  and 
it  is  with  reference  to  these  that  it  may  be  affirmed  that 
the  broad  rule  governing  the  inch  and  the  fiftieth  does 
not  hold  good. 

Some  four  or  five  years  since,  the  author,  in  writing 
to  a  brother  microscopist,  hazarded  the  statement  that 
the  time  would  surely  come  when  the  optician  would 
furnish  one-sixths,  capable  of  performing  all  the  work 
then  done  with  the  one-fiftieth.  The  principal  reason 
advanced  at  that  date,  in  support  of  his  opinion,  was, 

First,  assuming  the  case  of  a  perfect  objective  with  a 
perfect  eye-piece,  he  claimed  that  it  made  no  difference 
to  which  end  of  the  tube  the  power  should  be  applied. 

Second,  the  nearer  perfection  arrived  at  in  the  con- 
struction of  the  objective  and  eye-piece,  the  higher  may 
be  the  power  of  the  latter ;  and 

Third,  as  we  have  no  right  to  expect  absolute  per- 
fection in  the  construction  of  objectives,  it  nevertheless 
seemed  reasonable  to  infer  that  the  optician  could  bet- 
ter handle  and  adjust  a  lens  of  sensible  dimensions, 
such  as  are  used  in  the  manufacture  of  the  medium 


110  HOW   TO    SEE    WITH   THE    MICROSCOPE. 

powers,  than  could  be  possible  with  the  merest  speck 
of  glass  forming  the  fronts  of  the  one-fiftieth. 

Whether  the  ideas  thus  advanced  were  correct  or  not, 
the  fact  is  patent  that  in  less  than  two  years  from  the 
date  of  the  said  letter,  Mr.  Tolles  produced  a  one-sixth, 
that  excelled  for  any  and  all  work  the  performance  of 
any  one-fiftieth  on  record.  This  one-sixth  is  still  in 
the  possession  of  the  author,  who,  ere  the  glass  was 
thirty  days  old,  pitted  it  against  the  finest  fiftieth  to  be 
found  in  the  country.  The  battle  waged  for  an  entire 
week,  but  the  result  was  decisive.  It  was  David  vs. 
Goliath,  and  David  had  the  best  of  it. 

Scarcely  had  another  month  elapsed  before  Mr.  Tolles 
again  sent  the  writer  another  glass — this  time  a  tenth 
—  which,  in  turn,  eclipsed  the  previous  inimitable  work 
of  the  sixth;  while  at  a  still  later  day,  Mr.  Herbert 
Spencer  produces  a  tenth,  made  on  a  somewhat  differ- 
ent formula,  the  performance  of  which  is  not  excelled 
by  any  glass  yet  made,  "  be  it  a  fifth  or  a  fiftieth." 

Without  reference  to  the  "  impossible  180°,"  it  may 
be  positively  claimed  that  either  of  three  glasses  named 
have  greater  aperture  than  is  possible  (or  has  thus  far 
been  possible)  to  obtain  with  the  fiftieths. 

As  has  already  been  stated  in  the  introduction,  the 
writer  was  the  first  to  call  public  attention  to  the  claims 
of  American  objectives  of  medium  power.  Statements 
so  radically  at  war  with  the  generally  accepted  popular 
belief  were  destined,  as  a  matter  of  course,  to  meet  with 
opposition.  Microscopists  from  almost  every  section 
came  in  person  to  see  for  themselves,  many  of  them 


SOMETHING   FURTHER   ABOUT   OBJECTIVES.  11] 

bringing  their  favorite  high-power  glasses  for  compari- 
son, and  returning  to  their  homes  satisfied  with  the 
trip,  leaving  the  one-sixth  and  the  tenth  to  encounter 
the  next  comer. 

It  being  probable  that  there  are  others  who  yet  re- 
main to  be  convinced  as  to  the  accurary  or  validity  of 
the  claims  of  the  "  medium  powers,"  it  may  be  stated 
that  at  this  late  day  the  writer  is  no  longer  in  a  minor- 
ity of  one.  Microscopists  of  note  have  studied  the 
situation,  arriving  at  similar  results.  About  twelve 
months  ago,  Mr.  John  Mayall,  Jr.,  a  well-known  and 
talented  microscopist  of  London,  wrote  as  follows: 

"  I  am  not  going  to  enter  into  a  mass  of  details  of 
the  various  trials  I  have  made  with  Tolles'  one-fourth 
and  one-eighth.  Suffice  it  to  say  that  no  lenses  that 
have  been  in  my  hands  have  ever  been  so  thoroughly 
tested  against  the  best  lenses  by  English,  French,  and 
German  opticians  (here  Mr.  Mayall  presents  a  list  of 
seventeen  recent  immersion  objectives  by  the  most  re- 
nowned makers  in  Europe);  and  without  reserve  of 
any  kind,  I  say  these  lenses  are  the  finest  I  have  ever 
seen.  *  *  I  affirm,  then,  that  with  cen- 

tral and  oblique  light  on  all  the  objects  that  are  known 
here  as  tests,  Tolles  carried  the  palm.  I  find,  on  the 
most  severe  tests,  there  is  in  Tolles'  lenses  a  better  cor- 
rection for  spherical  aberration,  the  image  is  more  crisp 
and  clear.  By  difficult  tests,  I  mean,  for  instance,  sur- 
rirella  gemma  with  central  light,  or  amphipleura  pellu- 
cida  with  oblique  light.  I  urge  that 

low-angle  lenses  will  not  exhibit  the  definition  these 


112  HOW   TO   SEE    WITH   THE    MICROSCOPE. 

lenses  will  show,  and  that  if  one  takes  a  higher  power 
that  will  show  the  images,  he  will  find,  by  comparison, 
the  higher  power  will  be  the  more  difficult  to  manage. 
The  whole  question  tums  upon  results ;  if  you  are  con- 
tent with  medium  images,  use  medium  or  low-angle 
objectives;  if  you  train  your  eye  for  fine  images,  you 
must  use  high-angled  objectives." 

In  1876,  Dr.  J.  Gr.  Hunt,  of  Philadelphia,  a  widely 
known  and  expert  microscopist,  after  having  given  the 
new  American  objectives  of  medium  power  close  study, 
writes  as  follows ;  and  believing  that  the  doctor's  letter 
will  be  found  of  general  interest,  we  give  it  entire* 
The  glass  he  makes  reference  to  was  a  Tolles  tenth : 

"  I  can  now  report  to  you  that  the  one-tenth  you 
sent  me  is  grand.  It  contains  more  good  qualities  than 
are  to  be  -found  in  many  first-class  lenses — perfect 
mechanical  workmanship,  large  field,  gives  sharp  image 
on  the  margin  of  field,  decision  of  definition  leaving- 
nothing  doubtful  or  foggy,  equal  penetration  with  reso- 
lution; thus  being  superior  for  his tological  work. 

I  could  engrave  it  all  over  with  marks  of 
admiration.  .  .  .  For  the  best  work  of 
the  botanist  or  histologist  it  has  a  definition  which  can 
be  retained,  with  an  amplification  such  as  I  have  not 
seen  in  any  one  twenty-fifth  or  one-fiftieth  that  has  come 
under  my  notice.  ...  I  see  in  its  con- 
struction more  finger  skill,  more  time  and  conscious 
brain  patience  than  mathematics.  Hence  its  charac- 
ter; it  has  no  precedent,  but  is  wholly  original,  and 
unlike  any  other  ma&e,  English  or  continental." 


SOMETHING   FURTHER    ABOUT    OBJECTIVES.  113 

The  preceding  quotations  are  thus  presented  to  the 
reader  because  the  issue  we  have  under  consideration  is 
therein  discussed  typically  (I  may  say)  from  both  the 
American  and  English  standpoints.  To  the  testimony 
cf  these  talented  gentlemen  the  author  could,  did  his- 
space  allow,  add  a  mass  of  similar  evidence. 

I  repeat,  it  is  not  consistent  with  the  limits  of  this 
little  book  to  further  discuss  the  issue  in  question.  The 
author  therefore  dogmatically  asserts  that  his  positions 
taken  in  public  print  relative  to  the  matter  we  have 
been  considering,  were  then  correct,  and  have  so  re- 
mained up  to  the  present  date. 

But  mark  this  point:  the  claim  thus  established  in 
favor  of  "medium  powers"  of  the  widest  apertures 
has  no  reference  whatever  to  hosts  of  objectives  made 
and  sold  with  high-sounding  figures  attached.  Keep 
this  fact  in  lively  remembrance. 

We  are  now  prepared  to  return  directly  to  the  point 
from  which  we  started.  We  have  seen  by  our  digres- 
sion that  the  relations  existing  between  the  inch  and 
the  one-fiftieth  are  to  be  essentially  modified,  relatively, 
as  to  the  nature  and  performance  of  a  one-sixth  as 
compared  with  that  of  a  one-fiftieth.  For  instance,  if 
it  were  true,  as  has  formerly  been  accepted,  that  it  is 
the  province  of  the  inch  to  assist  in  the  study  of  the 
simpler  organisms,  and  that  of  the  fiftieth  for  the  in- 
vestigation of  the  mostjlelicate  structures,  it  does  not 
hold  good  at  this  present  writing  that  a  one-sixth  or 
tenth  (generally  classed  as  medium  powers)  are  the 
proper  objectives  for  an  intermediate  class  of  work  only. 

8  Microscopy. 


114  HOW   TO    SEE   WITH   THE   MICROSCOPE. 

It  is  obvious  also  that,  if  the  one-sixth  and  the  one- 
tenth  are  more  than  capable  of  doing  the  work  formerly 
set  apart  for  the  employment  of  the  one-fiftieth,  the 
former  have  the  better  right  tp  be  regarded  as  "high 
powers." 

Furthermore  it  occurs  in  the  present  advanced  stage 
of  optical  science  that  it  is  really  quite  impossible  to 
precisely  define  what  constitutes  a  "  medium  power " 
glass,  or  for  what  particular  class  of  work  would  such 
glasses  (if  defined)  be  characteristically  adapted.  The 
^author  confidently  believes  that  still  further  and  greater 
improvements  in  American  objectives  are  yet  to  be  ac- 
complished. He  believes,  too,  confidently  that,  as  the 
instrument  shall  approach  perfection,  and  still  higher 
«ye-pieces  be  brought  into  requisition,  he  may  yet  live 
to  see  the  Nobert  nineteenth  band  with  a  half-inch  ob- 
jective and  a  one-sixteenth  eye-piece.  It  therefore 
seems  to  him  that  any  discussion  as  to  the  characteristic 
duties  of  an  object-glass  based  entirely  on  the  focal 
length  of  the  same  may  wisely  be  dismissed  as  being 
(for  the  present  at  least)  impractical,  if  not  impossible. 

And  now  for  some  remarks  that  are  not  only  possible, 
but  can,  if  the  reader  elects,  be  made  eminently  practical, 
closely  related,  too,  to  what  has  just  been  written;  and 
in  these  the  author  hopes  to  render  some  service  at 
least  to  a  portion  of  his  readers. 

A  fine  objective  is  in  its  very  nature  a  costly  instru- 
ment, while  on  the  other  hand,  it  often  happens  that 
the  true  lover  of  nature  has  unfortunately  a  light  purse. 
In  fact,  this  whole  situation  is  to  be  regretted,  and  cer- 


SOMETHING   FURTHER   ABOUT   OBJECTIVES.  115 

tainly  to  be  ameliorated  if  possible.  It  happens,  too, 
that  the  so-called  "  high  powers,"  such  as  one-twenty- 
fifths,  one-fiftieths,  and  one  seventy-fifths,  cost  in  them- 
selves more  than  the  majority  of  observers  could  afford 
to  pay  for  an  entire  outfit,  and  thus  have  been  accessi- 
ble to  only  a  favored  few.  The  price  of  the  fiftieth,  as 
furnished  by  eminent  makers  may  be  quoted  at  from 
$250  to  $300.  I  dare  say  that  more  than  one  of  my 
readers,  earnest  workers  with  the  microscope  have 
yearned  time  and  time  again,  as  they  have  read  of  some 
wonderful  things  accomplished  with  a  twenty-fifth  or 
one-fiftieth,  for  the  means  to  enable  them  to  pursue 
similar  investigations.  Let  all  such  hail  with  joy  the 
announcement  that  these  costly  glasses  are  no  longer  a 
necessity,  and  that  their  work  can  be  not  only  done, 
but  better  and  with  greater  ease  accomplished,  with 
what  are  known  as  medium-power  glasses  of  wide 
apertures;  that  there  is  no  longer,  too,  any  necessity 
of  going  abroad,  or  paying  duties  thereby;  that  a  one- 
sixth,  or,  at  the  furthest,  a  one-tenth,  costing  from  £60 
to  $85,  will  (if  properly  selected)  compete  in  perform- 
ance with  any  one-fiftieth  extant — a  fact,  reader,  worth 
knowing. 

Another  dogma  in  the  popular  mind  has  very  general 
acceptance — to  wit :  that  angular  aperture  can  only  be 
obtained  at  the  sacrifice  of  working  distance.  The  old 
saying  is,  that  "  it's  a  poor  rule  that  won't  work- both 
ways;"  hence  it  should  obtain  conversely,  that  with  the 
sacrifice  of  working  distance,  angular  aperture  ought  to 
be  obtained;  but  this  is  not  always  the  case.  For  in- 


116  HOAV   TO    SEE    WITH   THE   MICROSCOPE. 

stance,  one -sixth  are  now  made  with  apertures  we  will 
say  (to  keep  out  of  controversy)  up  to  180°,  and  with  a 
working  distance  of  one-fiftieth  of  an  inch.  Now  the 
widest  angled  one-fiftieth  in  existence,  with  a  working 
distance  le^s  than  half  that  of  the  one-sixth,  will  be 
found  to  measure  less  than  170°,  and  in  the  latter  glass 
it  is  evident  that  working  distance  has  been  sacrificed 
without  corresponding  increase  of  angular  aperture.  The 
case  cited  is  an  instance  notably  in  point,  and  one  that 
cannot  be  dodged,  and  yet  to  a  certain  extent  the  same 
will  apply  to  some  of  the  intermediate  objectives. 
Take  again  the  befors-mentioned  sixth  of  the  widest 
angle  known,  and  its  working  distance  of  one-fiftieth  of 
an  inch.  It  will  be  found  that,  although  it  is  possible 
to  obtain  the  same  aperture  for  the  tenth,  the  working 
distance  will  sufier  decrease ;  and  here  again  is  another 
instance  where  sacrifice  of  working  distance  is  not 
accompanied  by  corresponding  increase  of  aperture. 

The  subject  is  by  no  means  exhausted,  and  is  well 
worth  a  little  ventilation.  We  can  better  get  at  the 
situation  by  supposing  a  case  which  might  possibly 
occur  in  practice.  Suppose  then,  reader,  that  you 
desire  five  one-inch  glasses,  each  glass  to  have  a  work- 
ing distance  of  five-tenths  of  an  inch,  and  each  to  mag- 
nify with  the  two-inch  ("A")  eye-piece,  fifty  diameters, 
and  that  you  gave  these  five  glasses  respectively  to  five 
opticians,  to  be  made  as  per  the  conditions  named. 
Now,  it  will  most  probably  occur  that  when  you  get 
these  five  glasses  in  hand,  the  working  distance  and  the 
magnifying  powers  of  each  are  true  to  the  specifications, 


SOMETHING   FURTHER   ABOUT   OBJECTIVES.  117 

and  further,  that  no  two  of  the  five  glasses  will  have 
the  same  angular  aperture. 

It's  well  enough  to  pause  here  and  allow  the  approach 
of  a  deluge  of  threadbare  argument.  Says  one,  "All 
this  proves  nothing.  It's  quite  possible  that  the  glass 
with  the  narrowest  aperture  may  be  the  better  corrected. 
Let  your  own  rule  be  here  applied,  and  the  quality  of 
the  apertures  tested;  nothing  short  of  a  competitive 
examination  can  be  determinate." 

To  this  the  writer  says  amen ;  but  the  reader  is  again 
reminded  that  this  is  nothing  more  or  less  than  "fight- 
ing objectives."  This  is  the  course,  too,  which  the 
author  has  pursued  in  the  way  of  making  competitive 
examinations  of  objectives  in  his  own  interests,  and  in 
behali  of  those  of  his  pupils,  his  friends,  and  his  corre- 
spondents. The  result  being,  in  nineteen  cases  out  of 
twenty,  that  the  glass  with  the  wider  aperture  proved  in 
every  other  respect  the  better  glass — a  result,  too,  not 
improbable  in  its  nature,  when  it  is  borne  in  mind  that 
those  of  our  opticians  who  have  given  great  attention  to 
the  development  of  aperture  are  no  ways  behind-hand 
in  their  general  professional  attainments. 

Again,  (to  steer  clear  of  cavil  or  controversy,)  suppose 
that  of  the  five  glasses  before  named,  all  having  the 
same  working  distance  and  amplification,  the  one  with 
the  lower  aperture  being  made  by  Mr.  X.,  and  the  other 
of  wider  angle  being  by  Mr.  Y.,  both  objectives  being, 
too,  equally  well  corrected.  That  such  a  condition  of 
things  is  possible  no  one  will  attempt  to  deny.  Here 
is  M  condition  to  which  the  popular  dogma  can  be 


118  HOW   TO    SEE    WITH   THE    MICROSCOPE. 

applied  to  advantage — to  wit:  we  can  send  to  Mr.  Y. 
for  another  inch  similar  to  the  one  in  hand,  but  with  a 
lower  aperture,  and  corresponding  to  that  of  Mr.  X., 
and  it  will  obtain  that  Mr.  Y.,  in  cutting  down  the 
aperture  of  his  inch  to  that  of  Mr.  X.,  will  increase  his 
working  distance;  and  here  (comparatively)  we  gain 
working  distance  without  loss,  or,  as  it  has  been  termed, 
sacrifice  of  angular  aperture. 

Hence  we  arrive  at  the  conclusion  that  the  function 
recognized  as  "angular  aperture  "per  se  is  not  a  fixed 
and  definite  quantity  nor  one  that  can  be  fenced  in  and 
subjected  to  any  fixed  rules.  Nothing  definite  in  the 
way  of  rigid  law  can  be  applied  to  it.  In  the  case  just 
mentioned,  another  curious  conclusion  might  be  arrived 
at,  and  justly  too.  For  instance,  the  decrease  of  aper- 
ture from  that  of  the  wider  aperture  to  that  of  the  lower 
would  not  only  be  accompanied  (accepting  the  popular 
dogma),  which  in  the  case  in  question  would  hold  true 
by  an  increase  in  the  working  distance,  but  the  penetra- 
ting power  of  the  glass  wrould  thereby  be  enhanced,  and 
this,  too  (comparatively),  without  loss  of  angle. 

The  facts  presented  are  valuable,  are  significant,  and 
worth  careful  thought  and  study.  The  author  has 
never  seen  them  in  print,  and  they  are,  as  suggested, 
the  result  of  an  active  experience. 

And  this  brings  us  to  the  consideration  of  another 
matter;  I  refer  to  the  popular  dogma  of  "penetration." 
This  has  been  the  biggest  toad  in  the  puddle,  and  has 
exercised  an  active  agency  in  roiling  and  mystifying  the 
mind  of  the  microscopist.  The  doctrine  of  penetration 


SOMETHING   FURTHER    ABOUT   OBJECTIVES.  119 

as  generally  taken  and  accepted  may  be  thus  stated: 
objectives  of  low  angular  aperture  are  endowed  with  a 
peculiar  inherent  and  intrinsic  power,  by  virtue  of 
which  they  enable  the  observer  to  see  and  study  struc- 
tures situated  .in  different  planes  of  the  object.  For 
example,  if  the  objective  be  focussed  accurately  to 
details  occupying  an  intermediate  plane  of  the  object  to 
be  examined,  then  will  the  low-angled  glass  allow  the 
observer,  without  change  of  focus,  to  study  other 
details  of  the  said  object,  situated  in  planes  either 
nearer  or  more  remote.  We  have  been  taught  that  this 
is  a  most  valuable  property,  and  one  due  to  the  employ- 
ment of  low  angles  only — the  idea  thus  conveyed  being 
that  the  low  angles  possess  a  peculiar  and  accommodat- 
ing power  of  great  value  to  the  microscopist,  to  which 
the  wide  apertures  stand  inflexibly  opposed,  and  defiant. 
In  support  of  the  doctrine  of  penetration ,  it  has  been 
customary  to  present  the  case  of  the  optical  principles 
governing  the  action  of  low  apertures,  contrasting  the 
same  relatively  with  similar  conditions  involved  in  the 
,  use  of  the  high  angles ;  thus  we  have  been  taught  that 
the  narrow-angled  glass  admits  as  a  matter  of  course, 
but  a  narrow  cone  of  light,  the  pencils  crossing  at  the 
focal  point  at  a  very  acute  angle.  Hence  it  is  "obvious" 
that  it  matters  not  whether  the  object  to  be  viewed  be 
placed  exactly  at  the  crossing  point  or  a  little  within  or 
without  the  said  focus.  The  accompanying  and  sup- 
posed increase  of  working  distance  attributable  to  the 
narrow  aperture  of  course  is  not  lost  sight  of;  and  we 
are  here  admonished  to  keep  in  mind  the  fact  that,  with 


120  HOW   TO    SEE    WITH    THE     MICROSCOPE. 

'an  infinite  working  distance,  there  would  be  no  need  of 
special  focal  adjustment,  and  hence  the  longer  the  work- 
ing distance  the  better.  On  the  other  hand,  we  are 
told  that  objectives  with  very  high  apertures  admit  a 
much  wider  cone  of  light,  the  lateral  rays  of  which  cross 
in  the  focal  point,  at  a  more  obtuse  angle,  and  hence 
the  necessity  of  placing  the  object  to  be  viewed  exactly 
in  the  local  plane.  On  all  other  planes,  nearer  or  more 
remote,  the  object  being  out  of  the  crossing  of  the  rays, 
cannot  be  well  defined;  and  here  again,  conversely  the 
presumed  decrease  of  the  working  distance  due  to  the 
increase  of  aperture  is  held  prominently  in  view. 

To  all  of  the  above,  which  has  proved  so  acceptable 
to  the  world  of  microscopists,  the  author  long  ago  pub- 
lished his  dissent.  He  never  did,  and  does  not  to-day, 
take  the  least  stocK  in  the  aforesaid  enunciation  of  the 
so-called  doctrine  of  penetration. 

Admitting,  as  in  the  case  of  the  two  objectives  pre- 
sented, that  the  cone  ot  light  illuminating  the  field 
from  the  high-angled  objective  is  wider,  and  that  the 
lateral  pencils  cross  in  the  focal  point  at  a  more  obtuse 
angle  than  can  occur  in  the  case  of  the  narrow-angled 
glass,  it  is  nevertheless  true  (and  singularly  this  little 
fact  seems  to  have  been  entirely  lost  sight  of),  that  the 
wider  cone  of  light  due  to  the  employment  of  the  wide 
aperture  includes  all  of  the  central  pencils  present  in  the 
case  of  the  narrow-angled  glass.  In  other  words,  there 
are  just  as  many  central  pencils  at  work  (and  remember 
that  these  are  the  fellows  that  cross  the  focal  plane  at 
such  an  acute  angle,  thus  furnishing  the  beloved  pene- 


SOMETHING   FURTHER    ABOUT   OBJECTIVES.  121 

tration)  in  the  making  up  of  the  wider  cone  as  can 
occur  with  the  use  of  the  narrow  aperture ;  furthermore, 
that  it  would  be  not  only  possible,  but  eminently  prac- 
ticable, by  the  use  of  a  diaphragm,  to  cut  clown  the 
cone  of  the  wider  aperture  objective  to  correspond  with 
that  of  the  low-angled  glass ;  hence  it  is  obvious  that  in 
this  latter  case  the  two  objectives  would  be  worked 
under  similar  conditions  as  respects  the  angle  at  the 
crossing  of  the  rays,  and,  applying  the  argument 
based  thereon,  neither  glass  can  be  endowed  with  the 
greater  penetration. 

Says  one,  "How  about  the  working  distance?" 
The  relations  of  angular  aperture  to  working  dis- 
tance have  already  been  discussed,  and  intentionally, 
with  the  view  of  preparing  the  mind  of  the  reader  for 
the  above  interrogatory.  But  there  remain  other  con- 
siderations bearing  on  the  matter  of  working  distance, 
and  the  clinching1  argument  on  the  part  of  the  writer 
remains  to  be  presented. 

In  doing  this,  the  author  is  compelled  to  deal  in 
assertions  dogmatically.  In  the  handling  and  compar- 
ing of  object-glasses,  he  has  had  a  very  large  experience, 
and  he  feels  that  he  has  the  same  liberty  to  speak  ex 
cathedra  as  has  been  granted  to  others.  Moreover, 
what  he  now  has  to  say  is  "  important  if  true,"  and  he 
is  as  well  assured  ot  their  correctness  as  of  any  other 
fact  within  his  knowledge  and  experience,  nor  is  he 
alone  in  the  matter  about  to  be  stated.  Without 
exception,  all  who  have  experimented  in  the  proper 
direction  assent  to  all  that  will  be  here  claimed,  while 


122  HOW   TO   SEE   WITH   THE    MICROSCOPE. 

those  who  have  not,  may  reasonably  be  expected  to> 
know  not. 

Let  it  be  required  to  display  an  object  under  the 
microscope,  and  under  a  given  amplification.  It 
matters  not  what  the  object  may  be — be  it  a  diatom,  or 
a  bit  of  voluntary  muscle,  or  what  not;  nor  dees  it 
matter  as  to  the  amplification — be  it  60,  600,  or  6000 
diameters,  as  the  case  may  be. 

Now,  to  attack  this  object,  we  will  provide  two  sets 
of  objectives,  including  all  the  focal  lengths,  say  from 
the  inch,  upwards,  to  the  one-fiftieth — these  glasses  to 
be  the  very  finest  of  their  kind  made  at  the  present  day, 
and  notably  of  low  apertures ;  the  other  set  to  be  simi- 
lar as  to  the  range  of  focal  length  and  quality,  but 
notably  to  possess  the  highest  apertures  (respectively)* 
known. 

Now  choose. your  object,  select  your  amplification,, 
and  display  the  former,  using  the  low  angles  with  their 
very  best  foot  foremost.  This  done,  allow  me  to 
remove  the  objective,  replacing  in  its  stead  the  suitable 
high-angled  glass,  and  I  affirm  pointedly  that  the  object 
shall  be  equally  well  displayed,  under  the  same  amplifi- 
cation, etc.,  and  by  an  objective,  too,  having  greater 
working  distance  than  the  low  angle  first  selected. 

It  should  be  contemplated,  in  any  competitive  com- 
parisons of  this  kind,  that  they  be  conducted  without 
prejudice,  and  solely  in  the  interests  of  science,  and 
when  so  conducted,  and  by  observers  fitted  for  the 
emergency,  the  author  apprehends  that  his  statements, 
will  be  found  correct. 


BALSAM    APERTURES. 

We  have  thus  again  endeavored  to  make  manifest 
that  the  idea  that  angular  aperture  is  accompanied  by  a 
sacrifice  of  working  distance  has  no  real  existence — 
that  is,  in  the  form  popularly  accepted. 

Thus  far  we  have  discussed  ' '  angular  aperture"  in  its 
popular  signification,  and,  in  several  of  its  aspects, 
from  the  definition  given  from  the  micrographic  dic- 
tionary. Taken  in  conjunction  with  the  remarks  we- 
have  thus  far  had  occasion  to  offer,  the  reader  would 
probably  infer  as  axiomatic  that  the  range  of  apertures 
would  necessarily  be  confined  within  the  axial  pencil 
and  the  one  striking  the  underside  of  the  slide  at  near 
coincidence,  thus  traversing  and  limited  by  an  arc 
measured  by  nearly  90° — the  latter  being  equal  to  180° 
of  aperture.  This,  too,  is  the  precise  aspect  to  which 
the  author  desired  to  restrict  his  observations.  Now 
there  is  another  kind  of  aperture  of  which  very  little 
is  generally  known,  we  refer  to 

BALSAM   APERTURES. 

From  a  theoretical  or  mathematical  standpoint,  the 
study  of  balsam  angles  fairly  bristles  with  difficulties; 
it  has  been  to  us  a  problem  to  which  our  school  boy 
wrestlings  with  Euclid  seem  a  pleasant  and  simple  exer- 
cise. While  we  frankly  admit  our  incompetency  to 
properly  present  the  subject,  we  have  to  remark,  on 
the  other  hand  that  we  were  not  willing  to  send  forth 
this  little  book  without  at  least  some  mention  of  the 
matter. 

Observers  interested  in  the  history  of  the  American 


124  HOW   TO   SEE   WITH   THE   MICROSCOPE. 

objective  (and  American  observers  ought  to  be,  to  a 
man)  will  find  the  subject  ably  discussed  in  the  columns 
of  the  London  Microscopical  Journal,  reference  being 
made  to  the  celebrated  controversy  on  the  subject  of 
angular  aperture  between  Mr.  K.  B.  Tolles,  of  Boston, 
Mass.,  and  Mr.  Wenham  of  London.  In  this  discus- 
sion, the  American  side  of  the  question  was  ably  assisted 
by  Col.  J.  J.  Woodward,  of  the  U.  S.  Army,  and  Prof. 
Keith,  of  Georgetown,  D.  C.  The  entire  controversy 
is  well  worth  reprinting  in  a  consolidated  form,  and 
should  find  an  appropriate  place  in  the  library  of  every 
American  observer. 

No  attempt  will,  tor  the  reasons  given,  be  made  to 
discuss  the  subject  of  balsam  apertures  in  these  pages. 
We  shall,  however,  try  and  give  the  novice  an  idea  or 
two  connected  with  balsam  angles  without  which  some 
things  which  will  hereafter  be  presented,  would  be 
wholly  unintelligible. 

Suppose  we  put  a  ray  of  light  down  the  tube  of  the 
microscope,  thus  reversing  the  usual  order  of  things, 
and  that  said  pencil  have  an  angle  of  41°.  This  pencil 
traversing  a  suitable  objective  in  position  over  a  bal- 
samed  mount,  will  find  emergence  into  air  at  90° ;  equal 
to  what  is  recognized  as  180°  of  aperture.  Such  an 
objective  would  be  said  to  possess  a  balsam  angle  of  82°, 
in  other  words  (rejecting  fractions),  the  balsam  angle 
of  82°  is  said  to  equal  an  air  angle  of  180°. 

Now  it  is  claimed  by  certain  American  opticians,  that 
it  is  possible  to  construct  immersion  lenses  that  are 
capable,  when  worked  over  balsam  mounts,  of  recogniz- 


BALSAM   APERTURES.  125 

\i\cr  interior  pencils  greater  than  41°.  Mr.  Tolles  claims 
for  some  of  his  recent  immersion  objectives,  balsam 
angles  as  high  as  120°.*  We  have  devoted  a  great  deal 
of  time  to  the  study  of  this  class  of  objectives. 

These  glasses  were  generally  known  here  at  home  as 
"  duplex,"  or  four  system  immersions,  as  distinguished 
from  the  older  form  having  a  single  front.  Many  of 
these  objectives,  ranging  in  their  claims  as  to  balsam 
angle  from  82°  to  100°,  have  passed  through  our  hands, 
and  have  been  submitted  to  close  and  careful  study ; 
one  object  on  our  part  being  to  determine,  if  possible, 
whether  a  glass  said  to  be  of  a  lew  balsam  angle  was 
in  any  respect  characteristically  different  from  another 
claiming  a  higher  balsam  angle,  and  in  this  way  to 
arrive  at  some  determination  as  to  the  existence  or  val- 
idity of  the  claims  resting  on  the  recognition  of  the 
an^le  itself. 

O 

As  a  result  obtained  from  close,  tedious  and  pro- 
tracted observations,  dating  from  the  present  date  back 
to  that  of  the  first  "  duplex"  made,  we  unhesitatingly 
affirm  that  it  is  quite  possible  to  distinguish  the  per- 
formance of  a  duplex  objective  of  82°  balsam  angle, 
from  a  similar  glass  of  100°,  otherwise  we  would  have 
had  no  occasion  to  have  introduced  the  subject  at  all. 

Now,  in  the  effect  of  balsam  aperture,  we  recognize 
in  the  high  balsam  angles  precisely  what  has  been  at- 
tributed to  high  air  apertures,  namely,  a  decrease  of 
working  distance,  as  the  balsam  angle  is  increased,  and 

*  Messrs.  Tolles  &  Spencer  are  now  (1880)  making  objectives  of  120°  balsam 
aperture. 


126  HOW   TO   SEE   WITH   THE   MICROSCOPE. 

a  corresponding  increase  of  definition,  when  worked  by 
•extremely  oblique  light  over  balsam  mounts  of  "  diffi- 
cult tests."  These  characteristic  differences  in  perform- 
ance are  so  palpable,  as  to  enable  us  to  select  in  less 
than  fifteen  minutes'  use  of  two  glasses  over  the  Moller 
probe  plate,  the  higher-angled  glass  (balsam)  from  the 
lower. 

It  has  been  claimed  by  some  who  have  used  the  duplex 
glasses,  that  the  higher  performance  by  central  light  is 
obtained  with  those  of  the  smaller  balsam  angle.  My 
•own  experience  does  not  authorize  me  to  endorse  these 
conclusions.  Certain  it  is,  that  when  the  higher  angles 
Are  used  by  central  illumination,  their  immense  power 
of  light  will,  if  the  matter  receive  not  proper  atten- 
tion, defeat  the  glass,  and  again,  even  with  oblique 
illumination,  the  high-angled  objectives  require  the 
most  careful  attention  and  expert  handling. 

We  are,  therefore,  prepared  to  endorse  to  some  ex- 
tent, referring  to  high  balsam  angles,  the  remarks  which 
have  been  quoted  from  "  The  Microscope  and  Its  Reve- 
lations." 

FLATNESS   OF   FIELD. 

It  is,  of  course,  desirable  that  an  object  known  to  be 
ilat  should  so  appear  when  viewed  under  an  objective. 
The  optician,  however,  has  thus  far  found  it  impossible 
to  secure  perfection  in  this  respect,  combined  with  the 
highest  aperture  obtainable,  and  this  might  be  urged  as 
an  objection  to  the  use  of  wide-angled  objectives.  The 
slight  error  shown  by  the  glasses  referred  to,  has  rn  uch 


FLATNESS   OF    FIELD.  127 

more  weight  on  paper  than  occurs  actually  in  practice, 
where  the  great  increase  in  definition  obtained  causes 
the  slight  deficiency  in  flatness  of  field  to  sink  into 
utter  insignificance.  Hence,  in  testing  the  qualities  of 
an  object-glass,  the  flatness  of  its  field  would  hardly  be 
•called  into  requisition. 

Nevertheless,  flatness  of  field  must  have  its  due 
weight,  and  the  performance  of  a  first-class  objective 
should  not  betray  any  serious  error.  It  will  be  well, 
then,  when  examining  an  objective,  to  look  after  the 
quality  referred  to. 

The  careful  testing  of  an  object  glass  in  this  particu- 
lar, is  not  such  an  easy  and  oft-hand  matter  as  might  at 
a  glance  be  presumed;  the  manipulator  may  arrive  at 
incorrect  results,  and  thus  condemn  a  glass  without 
due  cause  therefor,  and  a  word  or  two  as  to  the  proper 
mode  of  conducting  this  test  may  not  be  amiss. 

First,  it  is  of  the  first  importance  that  the  object  be 
in  itself  flat  when  presented  to  the  objective.  Errors 
may  creep  in — first,  because  the  object  is  not  in  itself 
flat,  or,  second,  because  it  is  mounted  on  an  improper 
slide,  or  on  the  cover  thereof — very  few  slides  are  flat, 
and  covers  are  notoriously  "  in  wind;"  third,  the  stage 
of  the  microscope  may  not  be  at  right-angles  to  the 
optical  axis,  and  fourth,  the  eye-piece  may  not  suit  the 
objective.  To  guard  as  far  as  possible  against  these 
sources  of  error,  proceed  thus  : 

Select  a  fine  itage  micrometer,  having  a  band  of  lines 
just  about  as  close  as  the  objective  can  well  display 
when  viewed  with  nearly  central  light,  and  if  you  have 


128  HOW   TO    SEE    WITH   THE   MICROSCOPE. 

no  conveniences  of  your  own,  take  this  to  the  machin- 
ist, or  the  watchmaker,  either  of  whom  will  allow  you 
the  use  of  a  steel  "  straight  edge,"  with  which  you  will 
be  enabled  to  ascertain  with  tolerable  exactness  whether 
one  side  of  the  micrometer  is  truly  a  plane.  This  clone, 
by  the  aid  of  a  suitable  "  guage,"  you  will  also  deter- 
mine as  to  the  other  face.  '  If,  in  a  process  of  this  kind 
the  micrometer  betrays  defects,  it  should  be  discarded 
and  another  one  chosen  in  its  place.  In  our  own  prac- 
tice we  always  use  a  Nobert  test-plate,  which  has  been 
found  to  be  very  reliable. 

To  avoid  the  third  source  of  error,  view  the  lines, 
selecting  as  close  a  band  of  lines  as  possible,  and  using, 
as  before  named,  nearly  central  light,  and  the  two-inch 
eye-piece,  with  the  micrometer  placed  horizontally  and 
vertically  on  the  stage,  examining  the  bands  from  end 
to  end  as  they  appear  in  the  field.  Repeat  the  experi- 
ment, but  reversing  the  micrometer  in  each  position  end 
for  end.  Any  error  due  to  the  pose  of  the  stage  is  thus 
made  manifest. 

Should  you  have  reason  to  suspect  trouble  from  the 
eye-piece  used,  repeat  the  entire  test  on  the  stand  of 
some  friend,  always  using  the  two-inch,  or  lowest  eye- 
piece. This  ocular  furnishing  the  more  severe  test. 

Finally,  let  it  be  known  that  all  the  eminent  makers, 
both  American  and  English,  furnish  glasses  that  are 
not  to  be  rejected  for  non-flatness  of  field.  We  would 
rather  trust  to  the  reputation  of  these  gentlemen,  than 
to  the  test  conducted  by  the  novice.  A  little  practice 
on  the  other  hand  on  the  part  of  the  latter  will  not  be 
a  waste  of  time. 


MOUNTING   OF   OBJECTIVES.  129 


MOUNTING    OF    OBJECTIVES. 

Having  glanced  briefly  at  the  optical  portion,  a  few 
words  in  reference  to  the  mechanism  of  the  instrument 
may  not  be  out  of  place. 

Adjustable  glasses  are  provided  with  movable  or 
stationary  fronts,  that  is  to  say,  in  the  process  of  re- 
volving the  correction  collar  the  front  lens  also  revolves, 
or  remains  stationary,  as  the  case  may  be.  The  station- 
ary front  being  the  mobt  expensive  mounting,  it  is  gen- 
erally adopted  in  first-class  American  or  London  glasses 
of  short  focal  distance. 

In  the  use  of  objectives  of  tolerably  long  focal  dis- 
tance, the  necessity  for  the  stationary  front  is  not  so 
apparent,  and  some  first-class  makers  adopt  either  form 
of  mounting  for  such  objectives.  It  behooves  the  buyer 
to  keep  in  mind  this  difference  in  the  cost  of  the  two 
mountings,  for  of  two  glasses,  both  equal  in  optical 
performance,  the  one  adjusting  with  stationary  front 
ought  to  be  the  most  costly. 

Generally,  the  mechanism  of  the  collar  adjustment 
should  be  first-class.  There  should  be  no  "slip,"  "back- 
lash," or  "  dead-point;"  the  collar  should  rotate  with  a 
certain  firmness  of  action,  and  yet  run  as  "  smooth  as 
oil;"  there  should  be  no  undue  rubbing  or  grating,  nor 
"hitch  or  hindrance"  of  any  kind.  With  a  one-half 
inch,  or  a  four-tenths,  a  slight  "  slip"  or  "  back-lash" 
need  not  defeat  an  otherwise  satisfactory  objective; 
but,  on  the  other  hand,  nothing  of  this  sort  can  be 
allowed  in  the  higher  and  first-class  objectives.  If  the 

9  Microscopy. 


130  HOW   TO    SEE   WITH   THE   MICKOSCOPE. 

collar  be  adjusted  by  the  maker  to  rotate  under  high 
pressure  only,  regard  this  with  suspicion,  and  examine 
for  back-lash  closely,  or  what  is  perhaps  the  better 
way,  get  the  opinion  of  a  skillful  mechanic. 

The  models  of  some  of  our  American  objectives  are, 
in  the  opinion  of  the  writer,  far  too  large  and  clumsy, 
and  the  fronts  too  large  and  too  flat.  We  decidedly 
prefer  the  conical  front  —  the  more  conical  the  better. 
The  new  tenth  of  Mr.  Herbert  Spencer,  which  we  have 
before  found  occasion  to  mention,  was,  beyond  all  cavil, 
the  most  beautifully  mounted  glass  we  had  ever  seen, 
and  in  which  the  last-named  objections  were  almost 
wholly  avoided. 

NOMENCLATURE    OF   OBJECTIVES. 

American  and  English  microscopists  usually  class 
their  objectives  on  the  basis  of  their  focal  length,  it 
being  arbitrarily  assumed  that  the  inch  s^lass  worked 
with  ten-inch  tube  and  with  two-inch  eye-piece,  should 
give  an  amplification  of  fifty  diameters.  Hence,  the 
half-inch  glass  would  give  one  hundred  diameters,  the 
one-fourth  two  hundred,  the  one-eighth  four  hundred, 
the  one-tenth  five  hundred,  and  so  on.  It  very  seldom 
happens,  however,  that  an  object-glass  will  exactly  re- 
spond to  the  designation  given  it  by  the  maker  —  some 
opticians  over,  while  others  under-rate  their  instru- 
ments ;  and  then  again  with  an  adjustable  glass  the  power 
will  change  in  different  positions  of  the  adjusting  collar, 
the  amplification  being  greater  with  the  systems  at 
closed  than  when  at  "open-point."  Even  when  due 


NOMENCLATURE    OF   OBJECTIVES.  131 

allowance  has  been  made  for  this  last  condition,  we 
have  seen  English  eighths  having  really  higher  power 
than  some  American  one-twelfths.  Again,  but  a  few 
weeks  since,  we  handled  a  foreign  one-sixth  which  was 
superior  in  amplification  to  a  Spencer  one-eighth.  We, 
here  at  home,  have  scolded  a  good  deal  at  this  state  of 
things,  and  at  times  have  rated  our  English  cousins  for 
thus  underrating  their  objectives.  It  is  quite  unneces- 
sary here  to  traverse  the  ground  we  have  already  dis- 
cussed, to  render  it  evident  that  as  the  objective  ap- 
proaches perfection,  these  nominal  distinctions,  based 
on  focal  length,  fail  to  have  particular  force.  If,  for 
example,  it  were  possible  to  produce  a  two-inch  objec- 
tive, which,  under  extremely  high  eye-piecing,  would 
more  than  do  the  work  of  our  present  tenths,  then  we 
could  afford  to  work  pretty  much  with  one  objective, 
and  to  the  eye-piece  look  for  the  determination  of  the 
power.  Until,  however,  some  such  "  possibility"  shall 
occur,  our  present  nomenclature  will  be  invested  with 
some  force,  no  matter  how  variable  this  force  may  be. 
It  is,  therefore,  desirable  sometimes  to  determine  the 
actual  rating  of  an  objective. 

The  method  usually  employed,  is  to  place  a  stage 
micrometer  in  position,  using  a  ten-inch  tube,  and  pro- 
jecting the  image  by  aid  of  the  camera  lucida  on  a  screen 
ten  inches  distant.  Knowing,  then,  the  actual  value  <of 
the  divisions  on  the  micrometer,  we  are  enabled,  by  the 
measure  of  the  magnified  image  thereof,  to  determine 
the  amplification.  This  method  is  so  well  known  and 
so  often  practiced,  we  content  ourselves  with  its  gen- 
eral mention. 


132  HOW   TO   SEE   WITH   THE   MICROSCOPE. 

The  method  has  its  drawbacks.  For  instance,  all 
microscopes  do  not  have  tubes  precisely  ten  inches  in 
length,  especially  when  the  objective  is  placed  in  posi- 
tion; and  then,  again,  if  the  problem  be  to  determine 
which  of  two  lenses  is  the  stronger,  it  may  occur,  and 
pretty  surely  too,  that  one  glass  will  have  a  shorter 
setting  i.  e.,  "mount,"  than  the  other.  There  are  ways 
to  dodge  the  difficulty,  but  the  best  method,  we  have 
seen  of  measuring  objectives,  where  strict  mathematical 
accuracy  is  not  a  vital  consideration,  is  by  the  use  of  a 
formula,  modified  by  Col.  J.  J.  Woodward,  and  by  him 
given  to  the  public  through  the  columns  of  Silliman's 
Journal  not  long  ago  (Vol.  III.,  June,  1872): 

Formula  : 

ML 


where  F  —  focal  length,  M  —  magnification  without 
field-glass  of  eye-piece,  and  L  —  length  between  stage 
micrometer,  and  micrometer  in  eye-piece. 

If  the  "B"  (one-inch  ocular  with  its  field-lens  re- 
moved, be  selected,  a  micrometer  ruled  to  one  six-hun- 
dredth of  an  inch  will  be  found  to  suit  it  very  well. 

It  will  be  seen  that  the  formula  is  extremely  simple, 
and  quite  within  the  comprehension  of  all  ;  we,  how- 
ever, append  an  example  or  two,  selecting  cases  which 
have  occurred  in  actual  practice. 

*  (1.)  We  lately  had  in  hand  a  glass  of  Mr.  Gundlachrs, 
made  for  a  half-inch,  and  we  desired  to  be  assured  as  to 
its  true  rating.  Placing  a  suitable  micrometer  on  the 
stage,  and  selecting  a  one-inch  ocular,  with  its  field- 
glass  removed,  but  fitted  with  micrometer  ruled  to  one 


NOMENCLATURE    OF   OBJECTIVES  133 

six-hundredths,  and  having  brought  the  lines  of  the 
stage  rnicrometer  in  focus,  we  then  measured  the  dis- 
tance from  micrometer  to  micrometer,  finding  the  same 
to  be  just  ten  inches,  and  on  comparing  the  divisions  of 
the  stage  micrometer  with  those  of  the  eye  -piece,  we 
found  those  of  the  stage  micrometer  to  be  amplified 
eighteen  linear.  Now,  working  out  the  formula,  and 
substituting  for  the  symbols  their  proper  values,  we 
have 


Focal  length=  =        =-5  in.  or  i  inch. 

19^  obi 

Hence,  we  find  the  glass  exactly  to  the  rate  given  it  by 
its  maker. 

(2.)  In  a  similar  manner  it  was  desirable  to  test  a 
(so-called)  one-fifth  objective.  Proceeding  just  as  be- 
fore, simply  changing  objectives,  we  measured  again  the 
distance  from  micrometer  to  micrometer,  getting  again 
just  ten  inches  —  a  matter  of  chance,  however,  and  one 
not  likely  otten  to  occur.  Comparing  the  two  microm- 
eters again,  we  get  an  amplification  of  the  stage  lines 
of  thirty-eight  linear.  Substituting  values  as  before 
we  now  have 

Focal  length  =  5§±12  =  J92.  =  .25  in.  or  *  inch. 


For  the  purpose  of  developing  the  capacity  and  value 
of  the  formula,  we  will  now  repeat  this  example,  but 
in  place  of  using  a  distance  of  ten  inches,  we  will 
arrange  to  secure  in  lieu  thereof  a  distance  of  twelve 
and  one-half  inches.  We  now  find  the  amplification,  as 
shown  by  the  two  micrometers  at  this  greater  distance, 


134 


HOW   TO   SEE   WITH   THE    MICROSCOPE. 


to  be  forty-eight  linear,  and  substituting  this  value,  we 
have 


Focal  length 


48+12-50  =   600 
2401 


=  ^-  =  "25  in.  again. 


Either  computation  gives  the  same  results  (rejecting 
fractions  too  small  to  affect  things  sensibly),  and  we 
see,  too,  that  the  glass  sold  for  the  one-fifth  is  really 
but  a  true  fourth;  and,  furthermore,  it  is  evident  that 
a  change  in  the  distance  of  the  two  micrometers  —  in 
other  words,  working  with  different  lengths  of  tubes — 
does  not  practically  affect  the  results. 

TABLE   OF  THE   MAGNIFYING  TOWERS   OF   SINGLE     CONV6X 

LENSES. 

The  first  column  gives  the  focal  length  for  parallel 
rays;  the  second,  third,  fourth  and  fifth,  give  the  mag- 
nifying powers  at  ten,  twelve  and  a  half,  twenty-five, 
and  fifty  inches  respectively,  the  last  three  being  from 
the  American  Journal  of  Science  and  Arts,  as  before 
mentioned,  while  the  second  was  computed  by  the  Hon. 
J.  D.  Cox,  of  Ohio,  and  by  him  presented  to  the 
author. 


Focal  Length 

Magnifying 

Magnifying 

Magnifying 

Magnifying 

lor 

Powers 

Powers 

Powers 

Powers 

Parallel  Rays. 

at  10  inches. 

at  lO1/^  inches. 

at  25  inches. 

at  50  inches. 

1 

2 

3 

4 

5 

3  inches. 

i*sn 

1-50 

6-17 

14-59 

2 

3-00 

4-00 

10-40 

22-95 

MAGNIFYING     POWERS. 


135 


1  1-2  " 

4-67 

617 

14-59 

31-30 

1 

8-00 

10-40 

22-95 

47-99 

2-3      " 

13-00 

16-69 

35-47 

72-98 

1-2      " 

18-00 

.... 

.... 

.... 

4-10    " 

23-00 

29-21 

60-48 

122-99 

1-4      " 

38-00 

47-99 

97-98 

197-99 

1-5      " 

48-00 

60-48 

122-99 

247-99 

1-6      " 

58-00 

72-98 

147-99 

297-99 

1-8      " 

78-00 

97-98 

197-99 

397.99 

MO    " 

98-00 

122.99 

247-99 

497.99 

1-12    " 

118.00 

147-99 

297.99 

597.99 

1-15    " 

148-00 

185.49 

372-99 

741-99 

1-16    " 

158-00 

197.99 

397-99 

797.99 

1-18    " 

178-00 

222-99 

447-99 

897-99 

1-20    " 

198-00 

247-99 

497-99 

997-99 

1-25    " 

248-00 

310.49 

622-99 

1247-99 

1-50    " 

498-00 

622-99 

1247-99 

2497-99 

By  the  use  of  the  preceding-  table  one  is  able  to  meas- 
ure the  focal  length  of  any  objective,  and  without  in- 
volving the  trouble  of  computations.  In  ordinary  cases 
it  will  be  only  necessary  to  see  that  the  two  microme- 
ters shall  be  exactly  ten  or  twelve  and  one-half  inches 
apart.  The  amplification  in  either  case  being  noted,  we 
enter  the  table  under  the  proper  head,  and  correspond- 
ing to  the  amplification  will  be  found  the  focal  distance. 
For  instance,  taking  the  first  case  we  have  presented, 


136  HOW   TO    SEE   WITH   THE   MICROSCOPE. 

that  of  Mr.  G-undlach's  objective,  we  worked  it  a  dis- 
tance of  ten  inches,  and  observed  an  amplification  of 
eighteen  linear.  Entering  column  two  of  the  table,  we 
find  at  a  glance  eighteen  to  be  opposite  to  focal  length 
of  one-half  inches. 

In  the  case  of  the  so-called  fifth,  with  the  two  micro- 
meters at  ten  inches  distance,  we  observed  a  magnifica- 
tion of  thirty-eight  linear ;  entering  the  second  column 
of  the  table  again,  opposite  thirty-eight,  we  have  the 
focal  length,  equal  one-fourth  inch.  To  the  last  com- 
putation we  worked  the  same  case,  but  with  the  micro- 
meters twelve  and  one-half  inches  distant ;  in  this  case 
observing  a  magnification  of  48.  Entering  the  table 
in  column  third,  opposite  to  47.99,  we  have  the  same 
focal  length  as  before,  viz.,  one-fourth  inch. 

It  often  occurs  that  many  first-class  stands  cannot  be 
worked  at  a  distance  of  ten  inches  with  objectives  of 
ordinary  lengths.  In  this  case  use  the  twelve  and  one- 
half  inch  distance,  which  can  always  be  obtained  by 
using  the  draw  tube. 


CHAPTEE  III. 

OBJECTIVES     CONTINUED. 

What  constitutes  a  really  superlative  wide-angled 
objective?  It  has  been  our  fortune  to  reply  to  this 
question  upwards  of  ten  thousand  times,  and  it  may  be 
true  that  no  two  of  these  responses  have  been  exactly 
alike.  In  the  present  essay  let  us  get  close  to  the  reader, 
introducing  a  little  gossip,  and,  at  the  same  time,  seek- 
ing a  little  relief  by  avoiding  expressions  which  are 
getting  to  be  stereotyped,  such  as  the  "  writer," 
"this,"  "  the  author,"  "that,"  etc.,  helping  ourselves 
freely  to  the  first  person  singular,  about  as  one  would 
when  writing  to  a  friend. 

It  has  been  already  shown  that  there  are  two  classes 
of  high-angled  glasses — namely,  those  having  balsam 
apertures,  say  up  to  100°,  the  other  class  responding  to 
•air  angles,  up,  say,  to  the  "  impossible,"  180°.  And, 
first,  let  us  consider  the  objective  ol  high  balsam  angle. 

I  have,  in  advance,  stated  that  these  glasses  necessa- 
rily have  a  very  short  working  distance.  But  this  re- 
mark must  not  be  swallowed  whole;  let  it  be  taken 
rather  with  a  "pinch  of  salt,"  keeping  this  little  fact 
well  in  hand,  that  there  are  wide-angled  balsam  aper- 
tures, having  greater  working  distance  than  will  be 
found  present  in  other  objectives  of  the  same  nominal 
focal  length,  and  having,  too,  no  really  wide  air  angles. 

137 


138       HO.W  TO  SEE  WITH  THE  MICROSCOPE. 

In  comparison  with  such  as  these,  the  high  balsam 
apertures  have  nothing  to  fear.  As  to  working  dis- 
tance, a  vast  amount  of  misguided  effort  has  been  ex- 
pended in  the  vain  attempt  of  trying  to  compare  one 
kind  of  an  objective  with  another;  for  instance,  a  wide- 
angled  air  aperture  with  objectives  of  narrow  air 
angles.  Hence,  we  have  had  nothing  but  muddle  and 
confusion.  I  repeat  what  I  have  before  printed,  that 
any  attempt  of  the  kind  is  as  futile  in  its  very  nature 
as  it  would  be  to  compare  a  "  turnip  with  an  orange." 
It  has,  therefore,  been  my  aim,  however  imperfectly  I 
may  have  succeeded,  to  lead  my  readers  along  one  road 
at  a  time,  and  this  "  objective"  point  has  been  steadily 
held  in  view  while  writing  this  little  book,  and  up  to 
the  present  writing,  whether  success  has  attended  the 
effort  or  not,  I  claim  some  credit  for  having  essayed  in 
this  direction. 

"  Revenons  a  nos  moutons." — I  repeat,  then,  that  of 
two  superlative  objectives  having  balsam  angles  ranging 
from  82°  to  100°,  the  rule  presented  holds  good,  i.  e., 
that  the  higher  aperture  will  have  the  shorter  working 
distance,  or,  in  other  parlance,  the  gain  in  aperture  will 
be  accompanied  by  a  sacrifice  of  working  distance. 

Now,  we  all  know  what  is  lost  with  the  decrease  of 
working  distance.  Let  us,  therefore,  seek  as  to  what  is 
gained  by  the  increase  of  aperture.  First,  we  gain  a 
wonderful  increase  in  intensity  of  definition;  an  increase 
in  definition  too,  entirely  unapproachable  from  any 
other  direction.  In  this  particular  these  glasses  stand 
alone  and  defiant.  Secondly,  their  immense  power  of 


OBJECTIVES    CONTINUED. 

light,  superlatively  corrected  as  they  are,  enable  them 
to  be  used  under  wonderfully  high  eye-piecing,  and 
with  comparatively  slight  loss  of  either  light  or  defini- 
tion, while  by  the  aid  of  these  high  oculars,  the  greatest 
magnifications  are  obtainable,  and  in  these  particulars 
also,  do  these  objectives  again  stand  alone  and  defiant. 
'  Somehow,  among  the  few  who  have  paid  attention  to- 
the  claims  of  the  balsam  apertures,  it  has  got  to  be  the 
popular  impression  that  it  is  the  particular  province  of 
these  objectives  to  bear  high  oculars,  the  impression 
having  force  in  a  restricted,  or  limited  sense  —  to  witr 
that  there  is  nothing  gained  really  by  the  use  of  high 
balsam  angles  under  low  or  medium  oculars. 

Any  idea  of  this  sort  is  totally  in  error,  for  even 
under  a  low  or  medium  eye-piece,  the  higher  balsam 
angle  will  demonstrate  its  presence  by  an  increase  in  the- 
intensity  of  definition,  while  its  greater  power  of  light 
is  in  itself  &  power  capable  of  being  turned  to  certain 
necessary  and  useful  purposes.  I  have  already  stated 
that  it  is  quite  possible  to  distinguish  the  one  glas& 
from  the  other,  and,  I  might  have  added,  "  under  low 
or  medium  oculars." 

But,  as  I  have  said,  with  all  this  gain,  there  is  an  ac- 
companying loss  of  working  distance.  But  this  is  not 
all;  those  who  have  been  accustomed  to  work  all  their 
lives  with  objectives  of  low  or  medium  apertures,  might 
with  good  reason,  claim  that  the  high  balsam  angle* 
are  "  exceedingly  inconvenient  to  use."  Palpable  is- 
the  fact,,  that  the  slightest  error  in  the  collar  adjust- 
ment, or  in  the  management  of  the  illumination,  will 


140  HOW   TO    SEE    WITH    THE    MICROSCOPE. 

suffice  to  defeat  the  maximum  performance  of  the  bal- 
sam apertures,  and  the  higher  the  balsam  angle,  the 
greater  the  "  bother  "  attending  their  use. 

Nor  is  there  anything  so  exceptional  in  all  this.  In 
any  instrument  of  precision,  when,  by  successive  im- 
provements, we  gain  width  of  effective  range,  and, 
simultaneously,  a  nearer  approach  to  accuracy  of  deter- 
mination, then,  in  ninety-five  cases  out  of  the  hundred, 
do  we,  in  like  manner,  increase  the  complications  of 
the  instrument;  thus  introducing  "  inconvenience  "  and 
"  bother,"  and,  be  it  known,  an  accompanying  call  for 
skilled  manipulators. 

We  often  hear  another  remark  —  to  wit,  that  those 
owning  and  using  the  class  of  objectives  we  are  now 
considering,  do  nothing  else  than  "  fight  them."  Before 
attaching  any  definite  force  to  this  remark,  it  will  be 
well  to  inquire,  "  for  what  purpose  is  ;.he  battle!"  Is 
it  to  determine  which  of  two  objectives,  differing  in 
construction,  but  supposed  to  be  nearly  alike  in  per- 
formance, is  the  better  one,  and  with  the  purpose 
(avowed  or  otherwise)  of  rendering  some  contribution 
to  a  scientific  end;  or  is  it  that  "A"  battles  "  B,"  the 
object  being  on  the  part  of  "A"  to  assure  himself  that 
his  glasses  are  not  behind  the  age  in  quality  of  per- 
formance; or,  again,  may  it  be  that  "  C,"  being  re- 
quested by  his  inexperienced  Iriend  "D"  to  select  for 
him  an  objective  in  every  respect  fully  up  to  the  times? 
Or,  to  mention  a  very  possible  case,  does  "E,"who, 
having  a  few  hours  of  daily  leisure,  desires  to  appro- 
priate the  same  to  the  study  of  object-glasses,  with  the 


SUPERLATIVE   WIDE-ANGLED   OBJECTIVE.  141 

view  of  perfecting  himself  in  the  manipulations  of  the 
same,  that  he  may  in  turn  render  his  observations  and 
experience  of  value  co  those  who  devote  their  spare 
time  to  investigations  with  the  instrument?  If  these 
are  the  ends  in  view  to  be  accomplished,  then  I  say, 
"  fight  objectives,"  and  furthermore  that  "  E"  need  rot 
be  ashamed  of  his  occupation.  On  the  other  hand,  if 
objectives  are  fought  for  other  and  baser  purposes,  that 
is  no  aflair  of  mine.  I  cannot  help  it,  and  the  objective 
is  not  to  blame. 

I  claim,  then,  that  the  high  balsam  angles  are  indis- 
pensable in  the  studies  of  the  advanced  investigator ; 
they  alone,  "  bother  or  no  bother,"  are  the  ones  for  the 
work.  Let  the  reader  keep  constantly  in  mind  that,  in 
the  study  of  difficult  and  delicate  structures,  the  slight- 
est superiority  of  definition  is  of  vital  importance.  A 
first-class  objective  of  high  balsam  angle  will  show, 
clearly  and  accurately,  details  in  an  object,  which,  from 
their  extreme  tenuity  or  transparency,  would  be  totalty 
invisible  when  viewed  under  an  objective  having  but  air 
angle. 

To  sum  up:  We  thus  arrive  at  the  conclusion  that 
objectives  of  high  balsam  angles,  have,  as  compared 
with  others  of  less  balsam  angle,  a  shorter  working  dis- 
tance, and  in  general  are  "  inconvenient  and  bother- 
some to  use;  nevertheless,  that  their  use  cannot  be  dis- 
pensed with  in  the  study  of  delicate  and  difficult  struc- 
tures, and  it  may  be  further  stated  that  these  are  the 
glasses  suitable  for  the  study  of  difficult  diatoms,  the 
display  of  the  Nobert  nineteenth  band,  and  the  like* 


142  HOW   TO    SEE   WITH   THE   MICROSCOPE. 

Thus  far,  whatever  force  may  attach  to  the  elements  of 
•"inconvenience"  and  "bother,"  of  which  we  have 
heard  so  much,  I  have  allowed  full  play  and  weight ; 
but  let  the  reader  not  lose  sight  of  the  fact  that  those 
accustomed  to  the  use  of  adjusting  glasses  never  aban- 
don them  to  return  to  their  h'rst  love,  nor  do  they  re- 
gard the  process  of  adjusting  a  superior  objective  as 
being  in  any  way  or  shape  a  "  bother"  or  "  inconven- 
ience." It  may  be  well,  right  here,  to  state  a  bit  of 
personal  experience.  I  am  in  the  habit  of  putting  ad- 
justing glasses  in  the  hands  of  my  pupils  at  the  earliest 
possible  moment ;  not  that  they  will  accomplish  more 
with  them  for  a  time  than  would  be  the  case  with  those 
non-adjustable,  but  in  order  that  the  pupil  be  early 
brought  in  contact  with  them,  and  thus,  by  degrees, 
get  accustomed  to  their  use.  By  adopting  this  course, 
the  tyro  learns,  in  due  and  proper  season,  an  important 
lesson,  to  wit,  that  there  are  some  things  to  be  done 
besides  putting  an  object  at  one  end  of  the  tube  and 
the  eye  to  the  other  in  order  to  see  what's  what.  Now, 
it  often  happens  that  there  may  be  more  pupils  in  the 
laboratory  than  adjustable  objectives,  and  thus,  per- 
force, a  student  or  two  will  have  to  fall  back  on  the 
non-adjustable.  When  this  state  of  things  occur  there 
is  inevitably  indications  of  discontent,  and  it  is  never 
on  the  part  of  those  pupils  occupied  with  the  adjustable 
objectives. 

So  much  for  the  "  inconvenience"  and  "  bother." 
Now,  let  us  get  after  that  other  elephant —  working 
distance.     I  have  granted  that  with  the  higher  balsam 


SUPERLATIVE    WIDE-ANGLED    OBJECTIVE.  143 

apertures  there  is  a  loss  of  distance.  Now  I  propose 
to  discuss  this  "  loss  "  from  a  practical  point,  and  in  so 
doing  shall  state  facts,  including  names  and  dates. 

On  the  22d  of  March,  1878,  I  received  from  Messrs. 
C.  A.  Spencer  &  Sons,  a  one- tenth  objective  of  high 
balsam  angle.  This  glass  was  made  to  my  order,  and 
for  the  Hon.  J.  D.  Cox,  of  Ohio.  Before  sending  it  to 
its  destination  I  "  fought  it."  Its  performance  was  as 
follows:  Worked  over  the  balsamed  Moller  probe 
plate,  on  the  Zentmayer  histological  stand,  with  the 
mirror-bar  swung  to  31°  from  axis,  I  saw  distinctly  the 
striae  of  Nos.  18  and  19  of  said  plate,  nor  had  I  any 
doubt  as  to  thus  seeing  the  No.  20,  the  illumination 
being  a  common  small  coal-oil  lamp.  The  light  was 
taken  direct  from  the  mirror. 

Worked  over  the  same  Moller  plate,  but  with  the 
Wenham  reflex  illuminator  (an  instrument  devised  for 
Shutting  out  all  pencils  having  air  transmission),  I 
saw  the  transverse  striae  of  the  No.  20  of  said  plate 
handsomely  using  powers  from  1,000  to  4,000  diam- 
eters. 

Tested  over  a  fine  slide  of  English  podura,  using 
ordinary  illumination,  and  nearly  central,  I  had  the 
finest  display  I  had  ever  witnessed. 

Worked  over  navicula  angulata,  with  "dead  central  " 
illumination,  it  gave  me  instantly  the  markings  very 
handsomely. 

Worked  over  a  dry  mount  of  amphipleura  pellucida. 
These  shells  surrendered  at  discretion ;  ordinary  oblique 
illumination.  Substituting  a  balsam  slide  of  this 


144  HOW   TO    SEE    WITH    THE    MICROSCOPE. 

diatom,  placing-  the  same  in  position  under  the  stage 
of  the  histological,  I  got  handsome  resolutions  with 
the  mirror,  at  say  80°  from  axis,  and  also  when  the 
swinging-bar  was  posed  so  that  more  than  half  the 
mirror  was  above  the  stage. 

Tested  for  working  distance.  I  found  the  same  to  bo 
.015,  equal,  say,  to  one-sixtieth  of  an  inch. 

There  were  very  many  other  "  rounds"  to  this  fight, 
which  are  purposely  omitted  as  having  no  bearing  on 
thes  subject  in  hand.  The  reader  has  before  him  the 
work  of  the  objective  by  central,  centrally  disposed, 
tolerably  oblique  and  decidedly  oblique  illumination. 

Now,  thus  having  the  work  of  the  objective  before 
us,  it  is  palpably  evident  that  it  has  all  desirable  work- 
ing distance.  Surely  no  one  but  a  bungler  would  at- 
tempt to  cover  a  nice  mount  with  glass  over  one  one- 
hundredth  of  an  inch  in  thickness,  while,  with  such  a 
cover,  the  one-tenth  will  have  plenty  of  room  and  to 
spare;  and  if  we  compare  the  glass  named  with  the 
usual  run  of  immersion  tenths,  it  will  be  obvious  that 
there  is  no  loss  of  working  distance  nor  any  sacrifice 
thereof  in  any  way,  shape,  or  manner. 

OBJECTIVES   OF  LOWER   BALSAM  ANGLE. 

These,  when  compared  with  the  glasses  we  have  just 
had  under  consideration,  will  be  found  to  have  greater 
working  distance,  as  has  been  before  stated;  and  with 
this  increase  of  distance  there  will  be  greater  focal 
depth  —  the  so-called  ll  penetration "  of  the  books. 
Now,  in  the  preliminary  investigation  of  many  objects, 


OBJECTIVES    OF   EOUEIl    BALSAM   A^GLE.  145 

this  is  a  desirable  quality  in  a  glass.  It  enables  us  to 
search  through  an  extemporized  mount  in  the  least  pos- 
sible time.  And  then,  again,  we  are  less  liable  to  allow 
important  details  of  structure  to  escape  our  attention. 
These  are  advantages,  and  must  be  recognized  as  such; 
but,  per  contra,  let  it  be  remembered  that  in  subse- 
quent examinations  it  often  becomes  quite  as  important 
that  this  quality  of  penetration  should  be  absent.  For 
instance,  when  it  is  desired  to  study  structures  situated 
in  one  plane,  and  one  plane  only,  the  less  of  penetra- 
tion the  better.  I  have  not  space  to  enlarge  on  this, 
but  let  the  reader  not  forget  the  fact.  The  glasses  of 
the  lower  balsam  apertures  are  really  the  easiest  to 
manage,  and  yet  are  effective  and  adequate  for  a  large 
class  of  work.  They  have  less  power  of  light,  and 
hence  do  not  "stand  up"  so  well  under  high  eye- 
piecing,  nor  have  they  the  same  exquisite  intensity  of 
definition.  In  a  certain  sense,  the  diminution  of  defini- 
tion is  very  slight,  indeed  scarcely  to  be  noticed  (if  at 
all)  when  examining  tolerably  vigorous  tests.  Hence, 
they  are  quite  adequate  for  the  resolution  of  nearly  all 
the  recognized  test  objects  when  mounted  dry.  It  is, 
then,  over  exceedingly  thin,  faint,  delicate,  and  trans- 
parent tests  that  the  higher  angles  assert  their  suprem- 
acy. 

If  the  general  definition  as  to  what  constitutes  a 
high-angled  objective,  given  on  a  preceding  page,  be 
accepted,  then  there  remains  room  to  discuss  a  class  of 
objectives  of  such  focal  lengths,  nominally,  as  defy  any 
expert  effort  on  the '  part  of  the  optician  to  extend 

10  Microscopy. 


146  HOW   TO    SEE    WITH   THE    MICROSCOPE. 

their  aperture  to  any  thing  like  an  approach  to  180°. 
Among  such  may  be  included  the  two  inch  of  25°,  the 
one  and  one-half  inch  of  37°,  the  one  inch  of  40°,  the 
two-thirds  of  45°,  the  one-half  inch  of  100°,  the  four- 
tenths  of  150°,  and  so  on.  All  the  glasses  above 
named  may  be  considered  as  high-angled  objectives. 
They  should  be  nicely  corrected,  fully  up  to  the  limits 
of  the  aperture  claimed  for  them,  and,  as  compared 
with  similar  lenses  of  narrow  apertures,  they  should 
possess  a  much  greater  power  of  light,  and  bear  higher 
eye-piecing;  and,  let  it  be  borne  in  mind,  that  ot  the 
above-named  objectives,  the  one  having  the  greater  dis- 
tance will  be  "endowed"  with  the  greater  "penetra- 
tion." 

And  right  at  this  place  let  us  see  what  the  "  power 
to  bear  high  eye-piecing"  means.  To  illustrate  this, 
we  will  take  a  case  such  as  might  happen  in  practice. 
For  example,  I  desire  to  see  the  transverse  lines  of 
pleurosigma  balticum,  and,  as  mounted  on  the  Moller 
balsam  test  plate,  their  striations  being  from  31  to  34, 
in  .001  Eng.  inch.  Now,  I  attack  this  with,  say,  a 
real  good  low-angled  one-half  inch,  and  find  that  I  can 
just  get  a  glimpse  of  the  lines  with  the  one-half  inch 
eye-piece.  I  then  apply  the  one-quarter  inch  eye-piece, 
and  find  that  the  view  is  not  nearly  as  satisfactory  as  it 
was  with  the  lower  ocular;  hence  I  conclude  that  the 
one-half  inch  eye-piece  is  as  high  as  the  objective  will 
bear.  Now,  removing  the  one-half  inch  objective,  we 
will  substitute  a  two-thirds,  but  of  higher  aperture. 
With  the  latter  glass,  using  the  one-half  inch  ocular,  I 


OBJECTIVES   OF   LOWER   BALSAM   ANGLE.  147 

get  better  shows  than  was  the  case  with  the  former  ob- 
jective, and  on  applying  the  one-quarter  eye-piece  I 
have  better  definition  yet.  There  is  some  loss  of  light, 
to  be  sure,  but  there  is  enough  left  to  do  the  work,  and 
in  a  more  satisfactory  manner  than  occurred  when  the 
lower  eye-piece  was  in  position.  I  take  this  case  as  an 
illustrative  one,  because  I  have  used  it  repeatedly  with 
my  visitors,  and  the  demonstration  has,  1  believe, 
always  been  accepted  as  satisfactory.  It  will  be  noticed 
that  thus  using  the  two-thirds,  the  power  applied  at 
the  eye-piece  was  greater  than  the  rating  of  the  objec- 
tive employed,  and  a  tolerable  test  for  an  object-glass  of 
such  low  nominal  power.  We  have  here,  then,  in  the 
experiment  cited,  an  illustration  of  what  may  be  said 
to  be  *'  power  to  bear  high  eye-piecing." 

There  is  a  general  and  indefinite  idea  afloat,  that 
there  is  something  about  high  eye-piecing  which  ought 
to  be  condemned.  Without  making  any  special  attack, 
it  may  be  admitted  that  observers  "came  honestly  by 
it."  The  facts  warrant  this  much:  power — z.  e.,  ampli- 
fication or  magnification  —  when  not  wanted,  is  to  be 
condemned,  and  it  matters  not  how  obtained,  whether 
at  one  end  of  the  tube  or  the  other.  On  the  contrary, 
if  any  thing  valuable  is  to  be  obtained  by  amplification, 
then  we  are  authorized  to  use  it,  and  to  the  best  advan- 
tage apply  it  at  either  end  of  the  tube,  as  the  case  may 
warrant.  There  seems  no  more  propriety  in  the  con- 
demnation of  high  eye-piecing  per  se  than  ought  to  ob- 
tain in  the  use  of  objectives  of  short  focal  length. 


148  HOW   TO   SEE    WITH    THE   MICROSCOPE. 


ADJUSTABLE    OBJECTIVES. 

The  generally  received  notion  in  regard  to  these 
glasses  is,  that  they  are  provided  with  an  adjusting 
collar,  so  that  they  may  be  "  corrected  for  aberrations," 
due  to  the  thickness  of  cover  employed  on  the  mount 
under  observation.  This  is  all  true  in  a  certain  sense, 
and  tc  a  certain  extent  only.  If  we  examine  the  same 
object  under  the  same  objective  (a  first-class  glass  of 
high  aperture),  but  through  covers  of  varying  thickness, 
we  will  find  that  the  very  best  performance  of  the  glass 
will  be  obtained  when  worked  over  a  particular  thick- 
ness of  cover,  and  that  any  change  from  this  particular 
thickness  will  interfere  with  the  performance  of  the 
lens,  no  matter  how  perfect  the  corrections  in  each  case 
may  be  made.  My  own  experience  teaches  me  that  the 
maximum  definition  is  only  obtained  when  the  objec- 
tive adjusts  at  or  near  that  point  in  the  collar  adjust- 
ment which  corresponds  to  the  maximum  aperture  of 
the  objective.  Now,  in  most  glasses  of  high  angles  the 
maximum  angle  will  be  found  at  only  one  position  of 
the  collar.  I  say  "  most  objectives,"  for  we  have  a 
one-tenth  made  by  Mr.  Tolles,  that  has  maximum  angle 
nearly  at  any  point  within  the  range  of  its  collar  ad- 
justment. We  have  also  a  one-sixth  by  the  same 
maker,  which  has  maximum  angle  only  at  the  "  closed 
point,"  the  aperture  decreasing  rapidly  as  the  collar 
approaches  "  open,"  and  with  the  decrease  of  angle  there 
is  an  accompanying  decrease  of  definition  and  effective 
force  of  the  objective. 


ADJUSTABLE    OBJECTIVES.  149 

Here  we  have  an  argument  in  favor  of  wide  angles 
which  has  been  in  the  past  quite  lost  sight  of,  and  was 
for  the  first  time  presented  to  the  public  by  the  writer 
in  one  of  his  monthly  contributions  years  ago ;  but  all 
this  is  foreign  to  our  present  purpose. 

Now,  in  the  case  of  the  one-sixth  of  Mr.  Tolles, 
should  it  be  attempted  to  use  this  glass  over  the  thin 
cover  of  the  Moller  probbe  plate,  the  result  would  only 
be  to  defeat  the  performance,  for  the  glass  would  "cor- 
rect" within  three  divisions  of  "open-point."  But, 
per  contrary,  if  we  desire  to  secure  the  best  definition 
of  the  said  objective,  and  over  the  said  plate,  it  becomes 
necessary  to  supplement  by  thicker  cover  (making  sure 
of  optical  contact  by  the  use  of  water  or  glycerine), 
until  the  glass  shall  "  correct"  at  or  near  "  closed." 

Hence,  it  occurs  that  it  is  essential  that  the  observer 
who  proposes  to  employ  objectives  of  wide  apertures 
should  pay  some  attention  to  the  condition  of  things ; 
that  he  should  know  precisely  over  what  covers  he  will 
be  enabled  to  get  the  maximum  performance.  In 
short,  to  ascertain  where  he  may  find  the  maximum 
aperture  of  his  objective. 

And  to  this  end,  we  propose  to  aid  and  assist,  as  far 
as  possible,  in  some  future  remarks  we  shall  have  occa- 
sion to  make  regarding  the  manipulations  of  the  objec- 
tive. During  the  past  twelve  years  the  author  has 
received  hundreds  of  letters  from  as  many  individuals 
commencing  the  study  of  the  microscope,  desiring  such 
information  as  to  the  best  way  of  making  an  invest- 
ment as  may  pertain  to  the  selection  of  stand,  objec- 


150  HOW   TO    SEE   WITH   THE   MICROSCOPE. 

tives,  etc.  The  said  letters  have  met  with  a  prompt 
response,  and,  as  has  before  been  stated,  perhaps  no 
two  of  these  have  been  alike.  In  each  and  every  case 
there  has  been  some  dissimilarity  of  circumstance,  or, 
on  the  other  hand,  we  have  suffered  some  change  in  our 
own  views.  Be  all  this  as  it  may,  the  experience  of  the 
last  two  years  enables  us  to  speak  more  precisely  to 
the  point  than  before,  and  we  now  endeavor  to  respond 
to  the  interrogatory — "  What  shall  I  procure  for  an 
outfit?" 

There  can  be  no  general  rule  that  will  apply  to  all. 
Let  us  take  the  following  as  a  typical  letter  for  con- 
sideration : 

"DEAR  SIR:  I  have  read  some  of  your  contribu- 
tions to  the  American  Journal  of  Microscopy.  .  .  . 
I  am  a  physician  of  ten  years'  practice ;  am  located  in 
a  town  of  some  ten  thousand  inhabitants.  I  am  satis- 
fied that  I  ought  to  know  enough  about  microscopy  to 
enable  me  to  examine  intelligently  urinary  deposits, 
cancerous  growths,  etc.,  and  to  this  end  do  I  propose 
to  purchase  the  necessary  equipment.  Any  informa- 
tion that  you  may  be  pleased  to  give  me,  will  be  with 
pleasure  received,"  etc. 

Now,  I  would  answer  this  letter,  and  did  answer  it, 
thus :  When  you  buy  a  stand  get  one  that  you  will 
have  no  occasion  to  sell  at  a  ruinous  sacrifice.  I  rec- 
ommend that  you  purchase  one  of  the  cheap  and  mod- 
erate-priced instruments,  and,  at  the  same  time,  one 
that  will  do  any  and  all  work.  Such  a  stand  ought  not 
to  cost,  with  one  eye-piece,  more  than  forty-five  dollars 


ADJUSTABLE    OBJECTIVES.  151 

(and  such  are  described  in  this  little  book).  Now,  as 
to  objectives.  You  can  do  all  the  work  named  with  a 
one-inch  of  tolerably  low  angle,  costing  you,  say,  some 
$7.00;  and  a  real  good  three-tenths  of  70°  aperture, 
which  will  cost  you,  say,  $11.00.  The  chances  are, 
however,  that  as  you  become  familiar  with  the  use  of 
the  instrument,  thereby  learning  its  value  to  you  in 
your  daily  professional  practice,  you  will  feel  an  inclin- 
ation to  dip  somewhat  deeper  into  the  problems  which 
will  most  assuredly  surround  you.  In  your  examina- 
tions of  urines,  you  will  get  glimpses  of  bacteria ;  you 
may  meet  with  structures  which  you  are  almost  assured 
are  "  pale  hyaline  "  tube  casts ;  and  you  naturally  desire 
a  little  more  amplification  and  definition  thereon  to 
enable  you  to  pronounce  with  certainty.  In  fact,  you 
now  want  such  a  glass  as  a  dry  one-fourth  of  110°  or 
120°,  and  adjustable.  Now,  to  use  this  glass  to  advan- 
tage, you  have  first  to  become  familiar  with  its  manipu- 
lations. It  will  be  requisite  that  you  arrive  at  some 
knowledge  of  this  before  such  an  objective  can  be  of 
much  avail  to  you.  Now,  if  you  purchase  the  one- 
fourth  recommended,  you  will  still  have  room  for  the 
employment  of  the  three-tenths,  but  you  will  have  to 
study  the  use  of  the  one-fourth  just  the  same  as  if  you 
had  never  seen  an  object-glass.  Hence,  I  had  rather 
recommend  that  you  purchase  the  one-fourth  at  the 
start,  and  thus  get  early  accustomed  to  the  use  of  ad- 
justable glasses ;  and  in  this  latter  case  it  will  almost 
assuredly  occur  that  you  will  eventually  desire  to 
employ  glasses  of  the  widest  apertures,  and  the  expe- 


152  HOW   TO   SEE   WITH   THE   MICROSCOPE. 

rience  you  have  gained  with  the  use  of  the  one-fourth 
will  be  of  the  utmost  value  to  you.  Moreover,  the 
one-fourth,  too,  will  continue  to  be  a  useful  interme- 
diate glass. 

And  thus  in  replying  to  all  my  correspondents,  I 
recognize  the  importance  that  one  and  all  shall  early 
become  acquainted  with  the  manipulations  of  adjusting 
glasses.  To  accomplish  this  they  must  use  objectives 
of  a  reliable  class,  i.  e.,  such  as  will  respond  promptly 
to  change  of  collar-adjustment,  keeping  well  in  mind 
tfye  importance  of  buying  nothing  to  be  discarded  or 
thrown  out  of  use  in  the  future.  In  the  case  under 
consideration,  it  will  happen,  in  nine  cases  out  of  ten, 
that  in  less  than  two  years  the  buyer  will  feel  that  he 
needs  a  first-class  inch,  or  perhaps  a  two-thirds,  in 
which  event  the  old  inch  will  be  of  great  service  as  a 
sub-stage  condenser,  providing  that  the  stand  has  been 
selected  with  this  end  in  view. 

It  may  further  happen,  in  truth  it  will  be  likely  to 
happen,  that  in  the  course  of  one  or  two  years,  my 
correspondent  will  either  push  his  own  observations  or 
desire  to  keep  pace  with  those  of  others,  and  over 
structures  of  the  most  delicate  and  "  difficult"  charac- 
ter, and  now  he  will  need  a  one-sixth  or  a  one-tenth  of 
the  widest  possible  aperture.  Allowing  this  to  occur 
he  will  have  expended  but  $110,  which  is  less  than  the 
usual  cost  of  a  nominally  first-class  one-sixteenth,  and 
all  the  glasses. on  hand  will  still  be  of  service.  Besides 
all  this,  he  is  well  armed  aud  equipped  for  any  work 
requiring  powers  from  50  to  5,000  diameters,  and  there 


ADJUSTABLE    OBJECTIVES.  153 

will  be  no  objectives  on  hand  that  will  not  be  worth 
their  cost. 

The  above  programme  seems  to  me  to  fill  the  bill 
as  well  as  any  other  that  could  be  named,  and  is  prac- 
tically the  same  as  that  followed  in  my  own  practice, 
having  daily  a  large  amount  of  work  over  urinary  de- 
posits, a  considerable  portion  of  which  does  not  require 
excessively  fine  definition,  and  time  being  very  much  of 
an  object,  I  employ,  in  addition  to  the  glasses  named,  a 
oheap,  but  good  and  reliable  half-inch,  say  of  35°  or  40°. 
With  this  glass  I  am  enabled  to  perform  much  prelimi- 
nary work  over  liquids,  and  am  able  to  dispense  with 
covers,  and  the  objective,  from  its  long  working  dis- 
tance, is  out  of  the  fumes  of  the  re-agents  constantly 
in  use.  The  half-inch  is  thus  of  great  service,  as  a 
time-saver  —  in  short,  as  a  convenience. 

Finally,  let  it  be  understood  that  I  have  no  war  to 
make  on  objectives  of  medium  apertures.  We  have 
stated  our  experience,  and  it  must  pass  for  what  it  is 
worth.  The  principal  point  which  I  desire  to  impress 
on  the  mind  of  the  reader,  is  that,  for  the  higher  class 
of  investigations,  the  objectives  of  wide  apertures  stand 
alone,  unapproachable  and  unexcelled ;  that  they  alone 
are  the  instruments  for  such  work,  and  this,  too,  regard- 
less of  the  character  of  the  illumination  employed,  be 
it  central  or  oblique.  Another  point  is  that  the  use 
of  the  high  angle  enables  the  observer  to  cut  down  the 
numerical  force  of  the  glasses  employed,  thus  saving 
unnecessary  expense.  We  wish  also  to  render  the  fact 
obvious,  that  a  wide  angle  glass  requires  time,  study, 


154  HOW   TO   SEE    WITH   THE   MICROSCOPE. 

and  attention,  and  that  the  manipulations  of  the  same 
are  not  acquired  in  a  day. 

In  iny  intercourse  with  microscopists,  I  have  nearly 
always  found  one  idea  salient.  The  general  question 
has  been  and  now  is,  «*  How  shall  we  contrive  to  save 
expense ;  where  can  we  buy  the  cheapest?  " 

It  seems  to  me  that  these  considerations  must  eventu- 
ally force  the  wide  apertures  into  use.  I  was  about  to 
say,  "There's  millions  in  it."  For  example,  we  know 
of  a  microscopist  who  has,  by  purchase,  from  time  to 
time,  acquired  a  batter}7  of  some  35  or  40  objectives. 
Now,  allowing  the  cost  of  these  to  average  $10  each  — 
not  a  high  estimate  —  the  owner  has  thus  paid  out  some 
$350  or  $400  for  objectives  alrne!  While  one-half  that 
money,  expended  in  glasses  of  the  highest  apertures, 
would  have  enabled  our  friend  to  have  accomplished 
any  and  all  work  that  can  be  effected  with  his  entire 
battery.  And  unless  I  am  greatly  mistaken,  the  wide 
apertures  would  carry  the  day,  and  with  flying  colors. 

This  is  no  solitary  case.  We  have  in  very  many  in- 
stances been  called  on  to  select  wide-angled  objectives* 
for  our  friends  and  correspondents,  and  in  each  and  every 
case — there  have  been  no  exceptions — we  have  received 
assurances  from  the  parties  interested,  that  there  would 
have  been  money  saved  had  the  facts  been  known  in 
time.  Says  one:  "  My  one-fifteenth  that  I  bought  two- 
years  ago  is  a  dead  letter;  what  shall  I  do  with  it?  I 
can't  sell  it  for  anything  like  what  it  cost,  it  would  be 
perpetrating  a  swindle !"  Says  another :  "  If  I  had  met 
you  thirty  days  ago  I  would  be  a  hundred  dollars  better 


ADJUSTABLE    OBJECTIVES.  155 

off  than  I  am  to-day ;  you  have  made  me  sick  of  my  ob- 
jectives." I  say,  therefore,  that  it  seems  to  me  that  this- 
string  must  pull,  to  the  end  that  the  microscopist,  who 
desires  to  invest  his  money  to  the  best  advantage,  will 
be  driven  to  the  use  of  the  wide  apertures,  no  matter 
how  strongly  he  may  have  become  prejudiced  in  another 
direction.  We  believe  and  earnestly  hope,  that  in  pre- 
senting the  subject  to  the  readers  of  this  little  work,  we 
have  done  them  a  good  honest  turn,  and  one  that  will 
be  appreciated.  . 

Before  entering  on  another  part  of  the  subject  of  this 
book,  we  desire  to  add  that  the  views  thus  set  forth  are 
the  result  of  practical  expeiience.  Here  is  no  specula- 
tion; but,  on  the  other  hand,  the  reader  has  before  him 
the  fruit  of  protracted  and  close  study.  The  time  was 
when  we  were  almost  alone  in  our  opinions,  but  that 
date  is  numbered  with  the  past.  Among  those  who* 
had  read  his  printed  articles  in  their  various  periodical 
forms,  and  have  subsequently  visited  him,  "  to  see  for 
themselves,"  he  can  name  many  of  his  dearest  friends* 
all  of  whom  have,  in  turn,  placed  the  writer  under 
countless  obligations.  And,  right  here,  by  the  way,, 
let  me  say,  that,  as  an  interesting  and  enjoyable  pastime, 
that  of  "  fighting  objectives  "  is,  when  occasionally  in- 
dulged in,  second  to  no  "  2.25"  race  on  record!  But 
of  any  of  the  good  things  of  this  world — "  enough  is  a 
feast." 


156  HOW   TO    SEE   WITH   THE   MICROSCOPE. 


EYE-PIECES. 

It  would  be  a  real  improvement  to  assign  to  individual 
eye-pieces  their  actual  power  expressed  in  inches,  and  to 
dispense  with  the  arbitrary  and  indefinite  nomenclature 
formerly,  and,  to  a  great  extent,  at  present  in  vogue. 
Thus,  let  the  two-inch  have  the  same  magnifying  power 
as  a  simple  lens  of  two  inches  focus,  and  similarly  as  to 
the  other  oculars  used.  Messrs.  Spencer,  Tolles,  Sidle, 
and  we  believe  Zentmayer,  adhere  strictly  to  this  plan. 

We  use  principally  the  inch,  half  inch,  and  one-fourth 
inch.  For  those  oculars  above  the  inch  in  power,  we 
greatly  prefer  the  solid  eye-pieces.  We  have  also  the 
two-inch  and  the  solid  one-eighth  inch.  The  former  is 
however,  but  very  seldom  used;  in  fact,  in  our  own 
practice,  it  is  seldom  wanted  or  even  thought  of.  The 
solid  one-eighth,  although  not  in  general  use,  cannot  be 
dispensed  with  when  working  with  sunlight  illumina- 
tion in  conjunction  with  objectives  of  high  balsam  angles. 
We  cannot  too  strongly  recommend  that  every  attention 
be  bestowed  as  to  the  quality  of  the  solid  oculars,  and, 
as  a  rule,  that  they  be  made  expressly  to  order. 

It  occasionally  happens  that  stands  fitted  with  poor 
objectives  are  placed  in  the  market  for  sale,  while  to 
accommodate  the  quality  of  the  objectives  the  powers 
of  the  oculars  are  let  down  considerably — thus  illus- 
trating the  truth  of  the  well-known  proverb,  c'est  le 
premier  pas  qui  coute. 

Let  the  purchaser  look  well  to  these  points  before 
consummating  an  investment. 


CHAPTER  IV. 

MANIPULATIONS — WENHAM?S   REFLEX  ILLUMINATOR. 

This  instrument,  and  its  various  modifications,  having 
come  into  very  general  use  in  this  country,  we  give  the 
following  cut  and  description,  taken  from  Dr.  Carpen- 
ter's work  on  "  The  Microscope  and  Its  Revelations:" 

"A  very  ingenious  and  valuable  illuminator  for  high 
powers  has  been  recently  devised  by  Mr.  Wenham,  and 
constructed  by  Messrs.  Ross.  It  is  composed  of  a  glass- 
cylinder,  half  an  inch  long  and  four-tenths  in  diameter, 
the  lower  convex  surface  of  which  is  polished  to  a  radius 
of  four-tenths.  The  top  is  flat  and  polished.  Starting 
from  the  bottom  edge,  the  cylinder  is  worked  off  to  a 
polished  face  at  an  angle  of  64°;  close  beneath  the  cylin- 
der is  set  a  plano-convex  lens  of  IJ-inch  focus.  When 
parallel  rays  are  thrown  up  through  this  apparatus  from 
the  mirror,  they  impinge  on  the  upper  surface  of  a  glass 
slide  at  an  angle  of  total  reflection ;  but  if  a  suitable 
object  adhere  to  that  surface,  the  light  reaches  it  on  an 
tingle  that  admits  its  passage.  The  object  is  then  seen 
brilliantly  lit  up  upon  a  dark  ground,  and  many  fine 
markings,  that  escape  notice  with  other  methods,  become 
very  distinct.  It  is  advisable  to  rotate  the  apparatus 
until  the  best  position  is  obtained.  Some  skill  and 
practice  are  required  to  use  this  apparatus  to  advantage, 
but  it  will  amply  repay  the  trouble  of  mastering  its 


158  HOW   TO    SEE   WITH   THE   MICROSCOPE. 

t  difficulties.  It  is  best  suited  to  thin  and  flat  objects ; 
with  those  that  are  thick  and  irregular,  distortion  is 
unavoidable.  Although  specially  designed  as  a  dark 


ground  illuminator,  good  effects  can  with  care  [and  by 
the  use  of  suitable  objectives],  be  obtained  for  such  ob- 
jects as  difficult  diatoms,  in  balsam  or  dammar.  But 
the,  effect  is  that  of  very  oblique  transparent  illumination" 
We  have  preferred  to  give  the  above  description  from 


WENHAM'S    REFLEX    ILLUMINATOR.  159 

Dr.  Carpenter.     The  interpolation  within  the  brackets, 
and  the  italics  are  our  own. 

As  is  above  set  forth,  this  instrument  was  designed 
by  its  maker  for  a  dark  ground  illuminator,  and  for  use 
with  high  powers;  was  made  and  sold  for  this  purpose, 
;and  was  generally  so  usad.  Shortly  after  their  intro- 
duction into  this  country,  Mr.  Samuel  Wells,  of  Boston, 
Mass.,  made  the  discovery  that  the  "reflex"  when 
worked  with  certain  very  high-angled  objectives,  could 
be  made  to  give  a  brilliantly-lighted  field,  accompanied 
with  beautiful  resolutions  of  the  severest  tests,  when  the 
latter  were  mounted  in  balsam,  the  effect  being,  as  Dr. 
Carpenter  most  justly  observes,  "  that  of  very  oblique 
illumination" 

As  is  evident  from  an  inspection  of  the  cut,  the  instru- 
ment can  be  variously  modified  in  its  working,  simply 
by  changing-  the  angle  of  the  facet.  The  fact,  too,  ap- 
pealed almost  simultaneously  to  all,  that  a  serious  objec- 
tion to  the  instrument  was  that  it  could  be  only  used 
over  balsam  mounts,  and  of  course  with  objectives  of 
the  highest  angles.  The  "reflex"  was  therefore  modi- 
fied by  the  London  opticians  to  suit  the  angles  of  their 
leading  objectives,  and,  at  the  same  time,  or  at  least 
shortly  after,  similar  modifications  of  the  instrument 
were  made  here.  There  has  been  an  effort  here  at  home 
to  claim,  on  the  part  of  our  opticians,  some  originality 
of  design  in  the  construction  of  these  various  modifica- 
tions. The  entire  plan,  however,  belongs  to  Mr.  Wen- 
ham,  and  the  simple  changing  of  the  angle  of  the  facet 
•does  not  authorize  any  claim  of  invention  The  author 


160  HOW   TO    SEE    WITH   THE   MICROSCOPE. 

has  used  several  of  these  instruments ;  the  first  one  wa? 
made  by  Mr.  Tolles,  the  angle  of  facet  being  26°  An- 
other one  made  some  little  time  afterwards  had  facet  of 
18°.  Subsequently  Messrs.  Spencer  have  made  him  sev- 
eral having  angle  of  15°.  The  genuine  instrument,  as 
made  by  Mr.  Wenham,  is  only  suitable  for  use  with 
objectives  of  high  balsam  angle,  while  those  of  the 
modern  form  can  be  employed  with  more  or  less  suc- 
cess in  conjunction  with  glasses  possessed  of  tolerably 
wide  air  apertures.  We  have  spent  a  great  deal  of  time 
in  the  study  of  this  instrument,  including  the  several 
patterns  named,  and  we  find  that  when  used  with  glasses- 
of  the  highest  balsam  apertures,  such  as  are  made  by 
Messrs.  Spencer  or  Mr.  Tolles,  and  over  the  severest 
tests,  such  as  amphipleura pellucida,  the  resolutions  are 
quite  as  strong  and  satisfactory  when  the  illumination  is- 
obtained  from  the  modified  "  reflex"  as  when  the  instru- 
ment described  by  Dr.  Carpenter  is  selected,  while  the 
latter  has  the  serious  disadvantage  of  being  adapted  for 
use  over  balsam  mounts  only. 

The  instrument  can  be  adapted  to  almost  any  good 
and  reliable  stand,  even  should  the  latter  not  be  pro- 
vided with  centring  apparatus;  yet  if  the  sub-staore 
collar  be  itself  well  centered,  a  little  ingenuity  on  the 
part  of  the  observer  will  secure  good  results.  It  is, 
however,  a  great  convenience,  when  using  the  "  reflex," 
to  employ  a  stand  allowing  the  sub-stage  to  approach 
the  slide  or  to  be  drawn  away  therefrom. 

To  use  the  "  reflex,"  place  it  in  the  sub-stage  fitting, 
select  a  low  power,  say  a  half-inch  or  a  two-thirds,  and 


WENHAM'S  REFLEX  ILLUMINATOR.  161 

one  that  you  know  centres  well  with  the  objective  to  be 
employed.  With  such  a  glass  see  if  the  central  mark 
placed  on  the  instrument  by  its  maker  occupies  the 
centre  of  the  field.  If  but  slightly  out  of  centre,  a  very 
slight  tipping  of  the  instrument  in  its  sub-stage  fitting 
will  often  be  all  that  is  necessary.  If  the  stand  has 
centring  screws  these  will  come  well  into  play.  We 
have  found  it  desirable  to  secure  perfect  centring,  and 
at  the  same  time  make  sure  that  the  plane  face  of  the 
facet  is  parallel  to  the  right-hand  edge  of  the  stage,  and 
adjacent  thereto.  Having  placed  a  small  drop  of  gly- 
cerine (which  is  preferable  to  water,  as  it  does  not  dry) 
on  the  top  of  the  facet,  and  having  placed  the  object 
and  slide  in  position,  the  "  reflex  "  is  made  to  approach 
and  the  glycerine  to  contact  the  slide.  It  is  better  not 
to  allow  the  top  face  of  the  instrument  to  actually  touch 
the  under  surface  of  the  slide,  still  keeping  it,  however, 
so  close  thereto  that  the  drop  of  glycerine  shall  be 
considerably  flattened. 

We  are  now  ready  to  screw  on  the  object-glass,  and  to 
make  immersion  contact  with  the  cover.  For  illumina- 
tion we  need  one  of  the  lowest  and  smallest  kerosene 
hand-lamps  that  can  be  found.  If  the  stand  is  small 
and  low,  it  will  become  necessary  to  place  it  on  a  suit- 
able box,  the  tube  inclined  to  a  convenient  angle.  Re- 
moving the  mirror,  u^e  the  light  direct  from  the  lamp 
keeping  the  latter  for  the  present  in  nearly  or  quite  a 
central  position.  If,  on  looking  through  the  eye-pie  se, 
there  be  found  a  lack  ot  illumination,  the  trouble  can 
be  rectified  by  moving  the  lamp  slightly.  Having 

11  Microscopy. 


162  HOW   TO    SEE   WITH   THE    MICROSCOPE. 

thus  got  light  enough,  next  proceed  to  find  your  object 
and  to  focus  the  same,  and  if  the  approximate  correc- 
tion for  the  objective  is  known  it  will  be  well  now  to 
apply  it. 

Next,  we  proceed  to  attempt  the  proper  display  of 
the  object,  Seize  the  lamp  with  the  right  hand,  turn 
the  edge  of  the  flame  edgewise  to  the  illuminator,  and 
move  the  lamp  bodily,  sliding  it  on  the  table  in  all 
directions,  to  the  right,  to  the  left,  towards  the  stand 
away  from  it.  If,  while  thus  manipulating  the  lamp, 
the  field  should  be  lighted  with  a  succession  of  colors, 
blue,  red,  green,  etc.,  you  may  be  pretty  sure  that  things 
are  working  well.  Making  sure,  now,  that  the  edge  of 
the  lamp  flame  is  turned  to  the  "  reflex,"  and  still  grasp- 
ing the  lamp  with  the  right  hand,  and  the  fine  adjust- 
ment with  the  left,  try  the  effect  of  very  small  move- 
ments of  the  lamp ;  these  will  be  followed  with  a  change 
of  color  in  the  field.  Supposing,  now,  that  the  distance 
of  the  lamp  from  the  stand  is  just  right.  We  will  find 
that  by  pushing  it  horizontally  and  parallel  to  the  front 
edge  of  the  stage,  towards  the  left,  we  shall  shortly  have 
a  blue  field,  while  with  a  little  further  shove  in  the 
same  direction  we  lose  our  illumination.  Now  it  is  in 
such  positions,  and  just  at  the  point  where  the  illumina- 
tion begins  to  decrease,  that  I  get  the  strongest  resolu- 
tions of  severe  tests.  If  we  now  retrace  the  path  of  the 
lamp,  carrying  the  same  towards  the  right,  the  field  will 
become  tinged  with  red,  and  by  pushing  the  lamp  still 
farther  thereto  this  will  deepen,  while  another  move- 
ment of  the  lamp  in  the  same  direction  will  cause  the 


THE   WOODWARD   ILLUMINATOR.  163 

illumination  to  die  away.  Now,  again,  good  resol utions 
can  be  obtained  in  the  red  similarly  to  those  in  the  blue, 
i.  e.y  just  at  the  point  where  the  illumination  begins  to 
decrease.  It  will  now  be  quite  time  for  those  who  have 
never  before  used  the  instrument  to  look  carefully  to- 
the  correction  of  the  objective,  and  for  the  trial  experi- 
ment the  object  selected  should  be  one  that  the  observer 
can  master  by  the  usual  oblique  illumination.  It  only 
remains  now  to  assure  ourselves  that  the  lamp  is  at  the 
proper  distance  from  the  stand,  which  is  accomplished 
by  simply  moving  it  farther  away,  or,  per  contra,  bring- 
ing it  nearer,  sliding  from  right  to  left,  and  trying  the 
red  and  blue  fields,  as  before  instructed.  The  very  best 
position  of  the  lamp  as  to  distance  is  generally  attested 
by  the  general  superior  brilliancy  of  the  illumination, 
together  with  the  fact  that  when  this  distance  is  just 
right  there  will  be  room  for  greater  lateral  play  of  the 
radiant  without  losing  the  illumination.  Care  should 
be  constantly  observed  to  keep  the  lamp  flame  exactly 
edgewise.  It  may  be  further  stated  that  when  things 
are  nearly  in  proper  position,  the  smallest  imaginable 
movement  of  the  lamp  will  often  produce  marked  effects. 

THE  WOODWARD  ILLUMINATOR. 

For  this  novel  and  useful  accessory  microscopists  are 
indebted  to  Col.  J.  J.  Woodward,  of  the  U.  S.  Army. 
A  paper,  giving  a  detailed  account  of  the  instrument, 
by  Col.  Woodward,  was  read  before  the  London  Royal 
Microscopical  Society,  and  subsequently  published  in 
the  London  Monthly  Microscopical  Journal.  The  paper 


164  HOW   TO   SEE    WITH   THE    MICROSCOPE. 

is  written  with  singular  tact  and  perspicuity,  and  is  here 
reprinted  unchanged: 

A.  Simple  Device  for  the  Illumination  of  Balsam-mounted 
Objects  for  Examination  ivith  certain,  Immersion  Ob- 
jectives whose  "Balsam  Angle"  is  90°  or  upwards. 
By  Surgeon  J.  J.  WOODWARD,  Brevet  Lieut.  Col.  U. 
S.  Army. 

[Taken  as  read  before  the  ROYAL  MICROSCOPICAL  SOCIETY, 

June  6, 1877.] 

"  Certain  immersion  objectives  are  so  constructed  that 
they  are  capable  of  admitting  rays  which  enter  the  front 
lens  at  a  greater  angle  with  the  optical  axis  than  the 
limit  for  dry  objectives.  That  this  is  not  only  theoretic- 
ally possible,  but  that  such  objectives  have  been  success- 
fully constructed,  was  several  years  since  demonstrated 
in  the  •* Monthly  Microscopical  Journal"  both  by  Mr. 
Keith  and  myself,*  notwithstanding  which  the  contrary 
has  often  since  been  energetically  asserted  by  writers  in 
the  same  Journal. 

"  Meanwhile,  immersion  lenses  possessed  of  the  exces- 
sive angle  in  dispute,  continue  to  be  put  into  the  market 
by  more  than  one  maker ;  and  perhaps  some  of  the  pur- 
chasers will  be  interested  in  a  simple  device  which  I  have 
used  for  some  time  with  such  objectives  to  illuminate 
test-objects  mounted  in  balsam.  This  device  consists 
merely  of  a  right-angled  prism  of  crown  glass  mounted 
beneath  the  stage  in  such  a  manner  that  its  long  side 
can  be  connected  by  oil  of  cloves,  or  some  similar  fluid, 

*June,  1873,  p.  268;  November,  1873,  p. 210.  March,  1874,  p.  119;  September, 
1876,  p.  124. 


r 


THE   WOODWARD   ILLUMINATOR.  167 

with  the  slide  on  which  the  object  is  mounted.  The 
details  of  the  plan  will  be  understood  by  the  diagram 
on  next  page,  in  which  the  glass  prism  is  seen  in  section 
just  beneath  the  object  slide  F  F.  Just  below  it  is  an- 
other right-angled  prism,  of  the  same  dimensions,  made 
of  brass;  the  section  of  this  prism  is  indicated  by  dark 
shading  in  the  diagram .  The  right-angles  of  both  prisms 
are  truncated,  and  the  facets  are  cemented  together  in 
such  a  manner  that  the  long  sides  of  the  prisms  are  par- 
allel. The  brass  prism  slips  transversely  in  a  groove  in 
the  top  of  a  holder,  C,  which  is  fitted  into  the  sub-stage 
of  the  microscope.  D  D  is  a  blackened  brass  screen 
held  in  position  by  two  brass  arms,  one  of  which  is 
shown  in  the  figure.  This  screen  is  parallel  to  the  adja- 
cent face  of  the  glass  prism,  and  has  in  it  a  small  cir- 
cular aperture,  E,  about  the  size  of  a  large  pin  hole. 
The  side  of  the  glass  prism  next  the  screen  is  covered 
with  black  paper,  in  which  is  a  corresponding  pin  hole. 
The  two  pin  holes  are  so  placed  that  a  beam  of  parallel 
white  sunlight  (r)  passing  through  both  will  be  per- 
pendicular to  the  sides  of  the  glass  prism  on  which  it 
impinges. 

"  To  use  this  apparatus  it  is  adjusted  in  the  sub-stage 
ot  the  microscope,  a  drop  of  oil  of  cloves  is  placed  on 
the  upper  face  of  the  prism,  the  glass  slide  F  F,  on 
which  the  object  is  mounted  in  Canada  balsam  under  the 
usual  thin  cover,  Gr,  is  placed  on  the  stage,  and  the  sub- 
stage  is  racked  up  until  the  drop  of  oil  of  cloves  is 
spread  out  into  a  thin  layer,  I. 

"  The  object  being  thus  arranged,  it  is  evident  that  if 


168  HOW  TO   SEE   WITH  THE   MICROSCOPE. 

a  beam  of  parallel  solar  rays  (white  sunlight),  reflected 
from  a  plane  mirror,  be  thrown  through  the  two  aper- 
tures upon  the  face  of  the  prism,  being  perpendicular 
to  that  face,  it  will  enter  and  pass  through  without 
refraction  until  it  reaches  the  upper  surface  of  the  thin 
glass  cover  Gr.  The  parallel  rays  impinge  upon  this 
surface,  as  is  evident  from  the  construction,  at  an  angle 
of  45°  with  the  optical  axis  O  O.  If,  now,  the  medium 
next  above  the  thin  cover,  Gr,  be  air,  this  obliquity  will 
be  greater  than  the  critical  angle,  and  total  reflection 
of  the  rays  will  take  place.  If,  however,  the  medium 
next  above  the  thin  cover  be  water,  the  obliquity  will 
not  be  greater  than  the  critical  angle.  Refraction  hav- 
ing taken  place,  the  rays  will  enter  the  water,  H ;  and 
if  an  immersion  lens  of  sufficient  angle  of  aperture  be 
focussed  upon  the  objects  mounted  beneath  the  cover  Gr, 
these  rays  not  merely  enter  the  front  of  the  objective,  but 
will  form  a  well-defined  image  of  the  object  on  a  brightly 
illuminated  field,  which  will  be  visible  through  the  eye- 
piece of  the  instrument  in  the  usual  way.  Of  course  it 
is  evident  from  the  diagram  that  with  no  dry  objective, 
or  any  immersion  objective  of  less  than  90°  balsam  angle, 
can  anything  whatever  of  balsam-mounted  objects*  thus 
be  seen. 

"  Immersion  objectives  may  be  divided  according  to 
their  behavior,  with  this  apparatus,  into  three  classes: 
1st.  Those  with  which,  since  they  do  not  have  sufficient 
angle  of  aperture  to  admit  the  illuminating  pencil, 

*  The  apparatus  can  be  used,  of  course,  to  secure  black-ground  illumina- 
tion of  suitable  dry  objects  if  they  are  mounted  on  the  slide  instead  of  the 
cover,  as  is  usual. 


THE   WOODWARD   ILLUMINATOR.  16i> 

nothing  can  be  seen,  precisely  as  in  the  case  of  dry  ob- 
jectives. 2d.  Those  which  have  sufficient  angle  of  aper- 
ture to  admit  rays  of  this  obliquity,  but  are  incapable  of 
bringing  them  to  an  image-forming  focus ;  with  these 
the  field  appears  well  illuminated,  but  the  objects  are 
not  well  defined.  3d.  Those  which  not  only  admit  rays- 
of  this  obliquity,  but  form  well-defined  images  with 
them.  To  this  class  belong  not  merely  immersion  ob- 
jectives with  the  so-called  duplex  fronts,  but  others; 
and  I  may  add,  not  merely  objectives  of  American  make,, 
but  some  constructed  by  a  well-known  English  house. 
As  might  be  expected,  the  quality  of  the  image  formed 
by  the  direct  rays  of  the  sun  thrown  through  a  pin  hole 
at  this  excessive  obliquity  varies  very  greatly  in  differ- 
ent cases.  I  will  state,  however,  that  I  have  thus  far 
found  at  least  seven  objectives,  some  of  English,  others- 
of  American  make,  which  define  sufficiently  well  under 
these  circumstances  to  resolve  Amphipleura  pellucida 
mounted  in  Canada  balsam.  With  the  objectives  which 
performed  best,  the  field  was  of  exceeding  whiteness 
and  brilliancy,  but  by  110  means  dazzling,  the  frustule 
undistorted,  and  the  striae  clean  and  black  on  the  white 
ground,  very  little  color  aberration  being  perceived. 
With  other  objectives  there  was  more  ot  less  color  aber- 
ration and  distortion,  both  which  faults  were  in  one  or 
two  cases  very  conspicuous,  although  in  the  part  of  the 
frustule  most  sharply  focussed  upon  the  striae  were 
handsomely  brought  out.  The  objectives  with  which  I 
thus  succeeded  ranged  all  the  way  from  one-fourth  to- 
one-sixteenth  immersion.  I  will  add  that  the  objectives- 


170  HOW   TO   SEE   WITH   THE    MICROSCOPE. 

which  resolved  Amphipleura  pellucida  under  these  try- 
ing circumstances,  when  used  in  the  ordinary  way  with 
this  or  other  test-objects,  displayed  an  exquisite  perfec- 
tion of  definition  which  it  would  be  hopeless  to  expect 
to  attain  with  objectives  of  less  angular  aperture. 

"  As  it  is  no  part  of  my  purpose  in  this  communication 
to  provoke  ill-tempered  discussion  of  the  merits  of  indi- 
vidual makers,  I  will  not  append  a  list  of  the  results 
obtained  with  the  various  immersion  objectives  I  have 
tried*  in  this  way.  The  apparatus  can  be  constructed 
for  a  few  shillings,  and  those  who  take  the  trouble  to 
use  it  will  soon  see  to  which  of  the  three  classes  any 
particular  objective  they  may  test  belongs." 

Subsequent  to  the  date  of  the  reading  of  the  preceed- 
ing  communication,  Dr.  Woodward  proposed  some  slight 
changes  in  the  form  of  his  prism.  Having  had  consid- 
erable experience  with  the  prism  as  now  used,  we  append 
the  following  description,  and  also  the  manner  of  work- 
ing the  instrument. 

Essentially,  it  consists  of  a  triangular  prism  of  crown 
glass.  In  the  form  adopted  by  Dr.  Woodward  the  ob- 
tuse angle  is  98°  and  the  two  acute  angles  41°  each. 

The  prism  may  be  used  unmounted,  by  simply  attach- 
ing the  same  to  the  under  surface  of  the  slide  containing 
the  objects  to  be  examined,  a  drop  of  glycerine  or  oil 
of  cloves  serving  to  secure  optical  contact,  and  at  the 
same  time  acting  as  cement  to  retain  the  prism  in  place. 
Notwithstanding  this  is  the  arrangement  employed  by 
many  observers,  it  is  but  a  faulty  plan,  in  fact,  a  regular 


THE    WOODWARD   ILLUMINATOR.  171 

"  make-shift "  arrangement.  With  the  prism  thus 
mounted  any  movement  of  the  object-slide  will  of  course 
cause  a  corresponding  movement  and  decentering  of 
the  prism;  furthermore,  such  object-slides  can  only  be 
Avell  examined  when  posed  in  nearly  the  horizontal 
position  on  the  stage;  it  often,  too,  occurs  that  the 
intermediate  drop  looses  its  hold,  suffering  the  prism  to 
slide  or  even  to  loose  its  attachment  entirely;  and  then, 
again,  I  have  frequently  got  the  very  best  work  when 
the  facet  of  the  prism  was  slightly  depressed  from  the 
under  surface  of  the  slide. 

It  is  far  better,  then,  and  for  the  reasons  given,  to 
have  the  prism  mounted,  and  to  those  who  propose  to 
adopt  my  method  of  illumination,  I  will  say  that  much 
depends  on  the  proper  mounting,  and  that  any  piece  of 
sub-stage  apparatus  which  shall  impede  the  passage  of 
rays  from  the  lamp  to  the  mirror,  or  from  the  mirror 
to  the  prism,  will  defeat  the  maximum  working  of  the 
latter.  Hence,  as  a  rule,  it  cannot  be  well  mounted  in 
the  usual  sub-stage,  the  latter  obstructing  top  much 

light. 

After  much  experiment,  and  with  the  hearty  co-opera- 
tion of  Mr.  Sidle,  I  am  now  in  possession  of  the  Wood- 
ward prism,  suitably  mounted  and  adapted  to  the  "  his- 
tological"  of  Mr.  Zentmayer,  as  will  be  seen  from 
inspection  of  the  cut  on  the  following  page. 

This  accessory,  as  above  delineated  in  plan  and  sec- 
tion, is  easily  placed  in  position  on  any  of  the  histolo- 
gical  stands.  Provision  is  also  made  for  centering  in  a 
lateral  direction.  The  prism  can  also  be  revolved  so  as 


172 


HOW   TO   SEE    WITH   THE   MICROSCOPE. 


to  use  either  angle.     It  can  at  will  be  raised  or  lowered, 
or  clamped  in  any  desired  position. 


o.    Vertical  vi*w. 

b.  Sectional  view. 

c.  Prism  three-fourths  full  size. 


In  the  adaptation  of  this  useful  accessory  to  the  acme 
stand  Mr.  Sidle  has  been  singularly  fortunate. 

This  neat  and  compact  little  device  screws,  as  I 
have  had  occasion,  on  a  previous  page,  to  state,  into  the 
well-hole  of  the  acme  stage.  It  is  thus  4<  on  and  off'" 


THE   WOODWARD   ILLUMINATOR.  173 

in  a  moment's  time.  All  the  necessary  motions  are  pro- 
vided for,  and  it  may  be  depended  on  for  first-class 
performance. 

From  what  has  already  been  stated,  it  is  almost  need- 
less to  repeat  that  when  either  of  the  mountings  de- 
scribed are  to  be  used  on  the  histological  or  acme  stands 
the  sub-stage  must  be  removed.  It  is  quite  possible  that 
the  mountings  presented  may,  with  slight  modifications, 
be  fitted  to  other  microscope  stands. 

The  form  of  prism  (angles  98°,  41°  and  41°),  as  sug- 
gested by  Col.  Woodward,  will  be  found  to  do  very 
acceptable  work.  It  occurred  to  me,  after  having  had 
considerable  experience  with  this  accessory,  that  there 
was  nothing  gained  by  having  the  acute  angles  equal, 
but  on  the  other  hand  advantages  would  be  insured  by 
an  inequality  of  these  angles,  either  of  which  might  be 
used  as  occasion  required.  I  therefore  begged  Mr.  Sidle 
to  make  me  a  prism  with  an  obtuse  angle  of  93°,  one  of 
the  acute  angles  to  be  47°,  the  other  to  be  40°,  and  this 
is  the  form  I  have  adopted,  believing  it  to  be  the  most 
seviceable  arrangement  yet  proposed,  and  especially 
adapted  to  the  general  run  of  modern  wide-apertured 
objectives.  To  provide  one's  self  with  two  or  more 
forms  of  prisms  will  not  involve  serious  expense.  Either 
of  the  mountings  I  have  described  can  be  modified  so 
that  the  prism  can  be  removed  and  others  substituted 
in  its  place. 

To  use  the  Woodward  prism — we  will  suppose  on  the 
acme  stand — first,  screw  the  accessory  into  the  well- 
hole  of  the  stage  securely;  next,  place  the  slide  to  be 


174  HOW   TO    SEE   WITH   THE    MICROSCOPE. 

examined  on  the  stage.  With  a  one  and  one-half  or 
two-inch  objective  (having  raised  the  prism  so  as  to 
contact  nearly  the  under  surface  of  the  slide),  focu& 
entirely  through  the  body  of  the  prism,  so  that  its  lower 
edge  may  be  seen  in  the  field,  and  by  turning  the  prism 
in  its  mounting  make  this  line,  by  estimation,  as  nearly 
vertical  as  possible.  If,  perchance,  this  line  appears  ta 
the  eye  considerably  to  the  right  or  left  of  the  centre 
of  the  field  there  is  no  harm  done ;  but  you  must  make 
a  note  of  the  fact;  this  would  indicate,  however,  that 
either  the  stage  is  out  of  centre,  or  the  mounting  of 
the  prism  has  been  injured. 

Next,  rack  back  the  objective  and  remove  the  slide, 
place  a  drop  of  glycerine  on  the  top  face  of  the  prism ; 
replace  the  slide  and  raise  the  prism  so  as  to  make  con- 
tact with  its  under  surface.  Having  made  this  contact 
exactly,  depress  the  prism,  say,  about  one-fiftieth  of  an 
inch.  Focus  again  with  the  low  power,  and  bring  the 
lower  edge  truly  vertical,  as  before  instructed. 

Eemove  the  low  power  and  substitute  the  wide-aper- 
tured  objective,  and  by  way  of  illumination  provide  a 
small  kerosene  hand  lamp,  the  flame  of  which  ought  not 
to  be  higher  than  two-thirds  the  distance  from  the  table 
to  the  stage  of  the  microscope;  remove,  also,  the  sub- 
stage. 

Now,  if  the  lower  edge  of  the  prism  was  seen  to  the 
right  of  the  field  place  the  lamp  to  the  right  of  the 
stage;  on  the  contrary,  if  the  edge  was  seen  to  the  left, 
pla,ce  the  lamp  to  the  left ;  and  in  either  case  swing  the 


THE    WOODWARD   ILLUMINATOR.  175 

mirror  away  from  the  lamp,  placing  it  so  that  the  gradu- 
ating wheel  shall  read  at  about  34,  35  or  36  degrees. 

The  lamp  being  passed  to  the  right  or  left  of  the  stage, 
as  the  case  may  be,  and  about  four  inches  distant  there- 
from, bring  the  edge  of  the  flame  to  the  mirror;  now 
move  the  lamp  to  or  from  the  front  edge  of  the  table, 
so  that  the  edge  of  the  lamp  frame,  prism  and  centre  of 
mirror  shall  form  approximately  a  straight  line  parallel 
with  the  front  edge  of  the  table, 

From  the  position  described  it  will  be  seen  that  the 
ordinary  sub-stage  would  be  entirely  in  the  way;  hence 
the  necessity  for  its  removal. 

Making  immersion  contact,  focus  your  objective,  and, 
without  changing  the  position  of  the  swing  bar,  manip- 
ulate the  mirror  so  that  the  field  may  be  nicely  illumi- 
ated,  select  your  object,  which  we  take  it  for  granted 
will  be  3ome  difficult  lined  test. 

Next,  interpose  the  large  bull's-eye  condenser  (flat 
side  to  the  lamp),  thus  concentrating  light  on  the  mir- 
ror ;  adjust  the  object  glass. 

It  will  be  well  now  to  try  the  effect  of  various  degrees 
of  obliquity,  remembering  that  any  considerable  move- 
ment of  the  swing- bar  will  necessitate  a  new  adjustment 
of  the  condenser.  A  slight  change,  too,  in  the  position 
of  the  lamp  will  sometimes  be  attended  with  excellent 
results,  keeping,  in  all  cases,  however,  its  edge  to  the 
mirror. 

The  above  includes  the  author's  method  of  working 
the  Woodward  prism ;  but  as  this  accessory  bids  fair  to 
come  into  general  use  he  will  now  traverse  the  ground 


176  HOW   TO    SEE   WITH   THE    MICROSCOPE. 

over  again,  feeling  sure  that  many  there  are  who  will 
not  object  to  some  further  discussion  of  the  subject. 

In  the  initial  attempt  to  use  the  prism,  the  observer 
should  select  an  object  (balsam  mounted)  with  which 
he  is  tolerably  familiar.  The  collar  adjustment,  also, 
should  have  been  previously  ascertained.  The  next  step 
is  to  decide  on  the  proper  position  of  the  radial  bar,  i.  e., 
its  distance  from  axis,  the  extent  of  this  distance  will 
be  demonstrated  by  the  illumination  becoming  too  feeble, 
the  images,  also,  becoming  generally  unsatisfactory.  The 
remedy  is,  in  such  cases,  to  cause  the  radial  bar  to  approach 
nearer  to  an  axial  position,  until  the  field  can  be  suffi- 
ciently lighted  and  the  object  displayed  with  tolerable 
vigor.  Thus  the  operator  has  the  means  of  "  gauging  " 
his  objective.  The  mirror  being  properly  posed,  it  re- 
mains to  obtain  the  best  possible  illumination,  which  is 
'effected  by  slight  changes  of  the  mirror,  condenser,  and 
finally  the  lamp.  When  things  are  generally  about 
right,  a  little  movement  of  the  lamp  (grasping  it  firmly 
by  the  bowl),  sometimes  twisting  it  to  the  right  or  left, 
so  as  to  get  the  flame  exactly  edgewise  to  the  mirror 
(which  is  best  determined  in  this  way),  will  result  in 
very  nice  effects,  bringing  out  the  stria?  on  such  tests  as 
the  Moller  test-plate  in  a  very  satisfactory  style. 

Resolutions  of  difficult  test  objects  are  accomplished 
with  this  illuminator  in  a  very  handsome  manner.  It 
is  an  easy  instrument  to  use,  and  will  adapt  itself  kindly 
to  the  objective,  of  course;  the  higher  the  balsam 
angle  of  the  object  glass,  the  better  the  definition.  It 
has,  in  its  ease  of  adaptation  a  decided  advantage  over 


THE   WOODWARD   ILLUMINATOR.  177 

the  Wenham  forms,  and  in  the  comparative  examina- 
tion of  objectives,  the  wedge  illuminator  is  an  exceed- 
ingly handy  accessory.  In  the  determination  of  the 
collar  adjustment  corresponding  to  the  point  of  maximum 
aperture,  the  same  holds  true. 

We  have  spent  two  or  three  entire  evenings  in  the  at- 
tempt to  determine  which  of  the  two  illuminators  is  the 
most  effective ;  and  our  experience  leads  to  the  conclusion 
that  the  "  reflex  "  is  somewhat  the  superior  instrument 
in  the  resolution  of  the  most  difficult  lined  tests;  never- 
theless, we  are  glad  to  give  the  newcomer  a  place  in  the 
accessory  box,  and  expect  to  make  it  very  useful.  It  is 
easily  made  and  mounted,  and  ought  not  to  be  expensive. 

Another  matter  closely  allied  to  the  new  illuminator 
may  as  well  be  mentioned  here.  Learning  that  the 
Messrs.  Spencers  had  just  completed  a  new  one-fourth 
inch  objective,  which  was  to  be  sent  to  the  Paris  Expos- 
ition, we  wrote  to  these  gentlemen  asking  the  loan  of 
the  glass  for  examination,  the  Messrs.  Spencers  re- 
sponded promptly,  and  it  occurred  that  we  received 
the  one-fourth  and  the  new  illuminator  the  same  day. 
We  were  thus  enabled  to  put  the  illuminator  to  practi- 
cal use  at  once,  in  this  manner:  First,  we  took  our  one- 
sixth,  working  it  with  the  illuminator  over  the  No.  20 
of  the  Moller  plate  getting  the  radial  bar  as  far  from 
axis  as  the  objective  would  allow  and  preserve  a  good 
display  of  the  striae.  This  done,  we  substituted  the 
one-fourth  in  place  of  the  one-sixth,  keeping  the  illum- 
ination, etc.,  carefully  in  the  same  position,  (the  cover 
of  the  plate  was  as  well  adapted  to  the  one  glass  as  the 


178  HOW   TO    SEE    WITH    THE   MICROSCOPE. 

other.)  We  found  at  once,  that  in  order  to  obtain  suf- 
ficient light,  and  retain  the  general  vigor  of  the  image, 
it  was  necessary  to  approach  the  radial  bar  to  the  axis 
-und  the  required  movement  of  the  latter  was  quite  per- 
ceptible. It  was  therefore  accepted  that  the  one-sixth 
faad  the  higher  balsam  angle.  The  question  then  turned, 
as  a  matter  of  course,  on  the  respective  working  dis- 
tances; that  of  the  one-sixth  was  known.  It  remained, 
therefore,  simply  to  measure  that  of  the  one-fourth, 
resulting  as  follows :  The  working  distance  of  the  one- 
sixth  is  twenty-four-thousandths  of  an  inch;  while  that 
cf  the  one-fourth  was  found  to  be  thirty-two-thou- 
sandths of  an  inch,  a  difference  of  33  per  cent  in  favor 
of  the  one-fourth.  Thus  it  will  be  seen  that  in  this 
instance  the  question  as  to  superiority  may  be  further 
taken  under  advisement.  We  relate  this  bit  ot  "  prac- 
tice" with  the  illuminator  in  illustration  of  the  pre- 
ceding remarks. 

One  thing  was  proven  even  by  the  above  experiment, 
to  wit:  Having  our  tenth  on  hand,  held  in  reserve  for 
especial  demands,  we  would  greatly  prefer  the  one- 
fourth  as  an  intermediate  s^lass.  This  fact  is  too  obvious 
to  need  further  comment,  and,  in  general,  we  are  glad  to 
add  that  the  new  one-fourth  of  the  Messrs.  Spencer  is 
indeed  a  lovely  glass,  and  if  properly  exhibited  in  Paris, 
will  be  an  honor  to  the  talented  makers. 

The  modified  illuminator  above  described  (obtuse 
angle,  98°,  acute  angles,  41°  each)  will  work  very  well 
with  objectives  having  wide  air  apertures  only;  hence, 
like  the  modified  "  reflex,"  it  will  work  over  dry  mounts, 


THE    WOODWARD   ILLUMINATOR.  179 

in  such  cases,  in  common  with  the  modified  "  reflex," 
its  action,  to  some  extent,  is  crippled;  nevertheless, 
nice  resolutions  are  to  be  obtained  with  either  instru- 
ment, with  either  of  which  we  are  able  to  instantly 
display  the  transverse  striae  of  amphipleura  pellucida, 
frustulia  saxonica,  etc.  The  simplicity  of  Dr.  Wood- 
ward's device,  its  ease  of  working,  and  the  facility  it 
affords  for  the  comparison  of  objectives  are  in  them- 
selves strong  points  in  its  favor,  and  to  these  may  be 
added  the  satisfactory  character  of  the  resolutions  ob- 
tained. We  gladly  accord  to  Dr.  Wood  ward  our  appre- 
ciation of  the  value  of  his  illuminator. 

We  are  informed  by  General  Cox  that  the  pin  hole 
apertures  are  only  used  when  working  with  sunlight 
illumination ;  they  also  serve  a  useful  purpose  as  an  assist- 
ance in  measuring  with  greater  precision  the  obliquity 
of  the  illuminating  pencils  employed,  thus  enhancing 
the  value  and  capacity  of  the  instrument. 


It  now  remains  to  present  to  the  reader  the  Tra- 
verse Lens,  devised  by  Mr.  R.  B.  Tolles.  The  follow- 
ing is  the  inventor's  own  description  of  this  valuable 
accessory,  and  is  taken  from  the  American  Journal  of 
Microscopy : 

6 '  With  the  advent  of  objectives  of  increased  interior 
angle  aperture,  the  indispensableness  of  equivalent  ac- 
cessory means  for  the  illumination  of  the  object  became 
immediately  evident.* 

*  See"M.  M.  J.,"  July,  1871,  p.  38. 


180  HOW   TO    SEE    WITH   THE    MICROSCOPE. 

"  III  my  first  construction  of  such  object-classes  I 
therefore  required  to  provide  means  which  proved  so 
suitable  that  I  have  adhered  to  their  use  to  the  present 
time. 

"The  first  appliance  was  a  deep  plano-convex  lens,  cen- 
trally mounted  below  the  object,  and  having  its  centre 
of  curvature  in  the  object  place.  Afterwards  I  adopted 
a  plano-cylindrically  convex  lens,  equal  to  a  hemisphere 
less  the  thicknsss  of  the  object-slide,  which  was  placed 
iji  immersion  contact  with  the  base  of  the  slide,  so  that 
the  object  itself  formed  the  centre  of  curvature  of  this 
illuminating  lens.  Around  the  convex  surface  of  this 
central  lens  moved  a  shutter  to  regulate  and  limit  the 

o 

access  of  light,  and  it  was  provided  also  with  a  small 
plano-concave  lens  which,  applied  by  its  concave  to  the 
convex  surface  of  the  larger  lens  by  immersion  contact, 
cancelled  the  refracting  surfaces  and  allowed  a  perpen- 
dicular beam  of  light  to  reach  the  suitably  immersed 
object  without  refraction.* 

"  The  device  in  a  more  complete  form  is  represented  in 
the  annexed  figure,  where  P  is  the  basilar  plate  of  the 
whole  traverse  system,  having  a  circular  groove  and 
track  in  which  the  carriage,  C,  moves.  On  a  projecting 
arm,  A,  of  the  carriage,  C,  are  mounted  whatever  ap- 
pliances are  to  be  used  to  modify  or  direct  the  light  upon 
the  traverse  lens,  T,  in  the  direction  of  the  object  at 
the  centre  of  the  system. 

"  In  the  figure,  the  concave  lens,  N,  is  shown  in  posi- 
tion on  the  arm.  Thus  situated,  the  interior  convex 

*  M.  M.  JM  May,  1873,  p.  213. 


TOLLES"  TRAVERSE  LENS.  181 

and  concave  surfaces  being  of  no  effect,  the  two  exterior 
plane  surfaces  of  the  traverse  system  constitute  it  a  prism, 
and  every  slightest  movement  of  this  concave  facet  lens 
on  the  traverse  lens,  T,  would  give  a  different  prism  to 
infinite  variety.  In  this  arrangement  the  concave  mir- 
ror can  be  used  in  the  ordinary  manner  and  condense 
light  enough  upon  the  object  for  all  ordinary  purposes. 
The  full  interior  aperture  of  a  dry  objective  would  be 
reached  at  the  very  convenient  obliquity  of  41°;  i.  e., 
at  less  than  the  critical  angle,  or  angle  of  total  internal 
reflection  between  crown-glass  and  air.  L  is  a  double 
convex  condensing  lens,  that  may  be  placed  at  about  its 
principal  focal  distance  from  the  object. 


"  For  a  condenser,  with  the  size  of  apparatus  as  drawn 
in  the  figure,  a  simple  lens  of  1J  inch  focus,  and  about 
ten  (10°)  degrees  of  aperture,  is  convenient,  and  if  the 
lens  is  movable  along  the  arm,  A,  it  can  be  focussed 
readily  on  the  object,  the  position  being  fixed  by  inspec- 
tion. This  would  be  well  for  parallel  rays.  If  diverg- 
ing rays  are  used  another  lens  of  two  or  three  inches 
focus,  mounted  on  the  arm,  A,  will  conveniently  take 


182  HOW   TO   SEE   WITH   THE   MICROSCOPE. 

up  the  rays  from  the  radiant  at  the  distance  of  the  focus 
of  this  supplementary  lens. 

"  The  plate,  P,  is  graduated  on  its  circular  edge,  as  in 
the  figure,  to  two  degrees,  and  the  arm,  A,  has  a  swing 
of  seventy  degrees  of  arc  each  way  from  the  axis  of  the 
microscope.  An  index-line  is  marked  on  the  bevelled 
edge  of  the  carriage  10°  from  the  axis  of  the  condenser, 
which  must  be  added  to  or  subtracted  from  the  real  ob- 
liquity of  the  illuminating  rays. 

"  It  is  obvious  that  any  observation  made  and  duly  re- 
corded as  to  its  conditions,  as  of  obliquity  of  incidence 
of  illuminating  pencil  or  ray,  form  of  the  pencil  or  beam, 
focal  length  and  distance  of  the  condenser,  such  obser- 
vation could  be  successfully  repeated.  The  record  of 
the  obliquity  of  the  most  oblique  rays  reaching  the  ob- 
ject directly,  and  giving  view  of  it  at  the  eye-piece  with 
luminous  field,  would  express  the  'balsam'  aperture, 
or  more  correctly,  the  half  interior  aperture  of  the  ob- 
jective when  the  front  lens  of  the  objective  and  the 
traverse  system  are  of  glass  of  similar  refraction. 

"  Having  thus  the  '  balsam '  angle,  we  readily  calcu- 
late or  learn  the  corresponding  angle  for  glycerine, 
or  water,  or  any  medium  of  which  we  have  the  index 
of  refraction.  A  corresponding  notation,  perhaps  for 
air,  might  be  engraved  in  juxtaposition  on  the  basilar 
plate." 


CHAPTER  V. 

ILLUMINATION. 

Ordinary  daylight  is  the  cheapest;  and  for  a  great 
many  purposes  the  microscopist  will  find  it  amply  suffi- 
cient. It  will  be  found  a  great  convenience  to  have  the 
light  enter  the  room  considerably  to  the  left  of  the 
microscope,  in  which  case  we  naturally  adjust  the  mirror 
with  the  right  hand.  Placing  the  instrument  directly 
before  the  window  is  objectionable,  and  such  a  position 
should  be  avoided  if  possible.  The  quality,  as  well  as 
the  quantity  of  daylight  illumination  will,  as  a  matter  of 
course,  vary  with  the  particular  aspect  of  the  day.  In 
bright  sunny  weather  the  light  from  a  white  cloud,  as 
has  often  been  recommended,  is  pure  and  pleasant  to 
vvork  with,  and  can  be  used  with  tolerably  high  ampli- 
fications with  good  success.  In  cloudy,  rainy  weather 
it  is  still  quite  possible  to  work  with  powers  up  to,  say 
200  diameters.  The  recent  introduction  of  the  swing- 
ing sub-stage  has  worked  somewhat  of  a  revolution  in 
our  own  practice.  For  years  we  have  steadily  eschewed 
the  achromatic  condenser  as  being  a  costly  and  incon- 
venient affair,  making  more  "  bother"  than  it  was  worth. 
The  principal  objection  I  had  to  urge  against  its  use  was 
that  it  was  a  fixture  beneath  the  stage,  thus  preventing 
me  from  varying  the  obliquity  of  the  illumination  at 
will,  as  I  desired,  and,  as  a  rule,  practically  I  got  better 

183 


184  HOW   TO    SEE    WITH   THE   MICROSCOPE. 

effects  without  than  with  it.  The  former  condensers 
were  generally  of  short  focal  length,  and  of  consider- 
able aperture.  In  the  late  stands  having  swing  sub- 
stages,  it  being  possible  to  swing  sub-stage  and  con- 
denser together  bodily,  there  seems  to  be  no  further  use 
for  condensers  of  wide  angles,  while  on  the  other  hand 
one  is  enabled  to  use  in  the  place  thereof  cheaper  and 
much  less  expensive  instruments,  and  the  lower  the 
angle  the  better,  and  one  need  not  be  very  particular 
as  to  the  matter  of  achromatism. 

On  commencing  the  use  of  the  little  Histological,  it 
occurred  to  the  author  (and  probably  to  scores  of  others) 
that  its  swinging  stage  was  a  strong  invitation  to  experi- 
ment again  with  sub-stage  condensers,  not  for  the  pur- 
pose of  resolving  difficult  tests  by  extremely  oblique 
illumination,  for  in  this  work  the  achromatic  condenser 
is  of  no  manner  of  account,  but,  per  contra,  it  seemed 
obvious  that  by  the  use  of  a  narrow  apertured  lens 
placed  below  the  stage,  and  so  arranged  that  its  inclina- 
tion might  be  changed  at  will,  good  effects  might  be 
secured  in  two  directions :  First,  by  the  concentration 
of  a  narrow  cone  of  light  immediately  upon  the  partic- 
ular portion  of  the  object  under  examination,  thus  en- 
abling the  observer  to  sharply  illuminate  a  certain  point 
of  his  object,  and  with  less  danger  of  drowning  out 
details  in  a  general  flood  of  light.  Secondly,  such  a 
contrivance  would  do  good  service  by  daylight  in  dark 
and  rainy  weather.  It  required  but  few  experiments  to 
demonstrate  that  there  was  force  in  the  above  reasoning, 
and  the  next  thing  in  course  was  to  ascertain  what  par- 


ILLUMINATION.  185 

ticular  form  of  condenser  would  be  the  best  adapted  for 
the  purpose. 

In  determining  how  far  it  would  be  practicable  to  cut 
down  the  angle  of  the,  condenser,  thus  reducing  the 
illuminating  cone  of  light,  we  have  made  countless  ex- 
periments, while  the  low  stage  of  the  Histological  ren- 
dered it  imperative  that  the  focal  length  of  the  lens 
should  be  such  as  would  best  accommodate  the  little 
stand.  To  sum  up  all  these  trials,  we  find  that  the 
cheapest  inch  objective  made  by  Mr.  Grundlach,  or  the 
inch  of  the  Messrs.  Beck's  "  National  Series,"  are,  either 
of  them,  well  adapted  for  the  purpose.  Mr.  Gundlach's 
inch  has  a  rubber  front  which  can  be  removed,  while 
the  setting  of  the  Beck  "  National "  is  extremely  short, 
and  thus  suited  in  this  respect  for  the  purpose. 

This,  then,  is  the  author's  arrangement  for  work  with 
low  or  moderate  powers  by  daylight  illumination,  and 
the  condenser  described  has  become  almost  a  fixture. 
In  the  darkest  days  there  will  be  plenty  of  light,  using 
the  concave  mirror,  while  in  bright,  sunny  days  the 
plane  can  be  substituted.  The  general  amount  of  illu- 
mination can  be  changed  at  will  by  merely  raising  or 
lowering  the  sub-stage,  and  the  nicest  effects  in  the  way 
of  definition  obtained.  The  swing-bar  can  also  be 
placed  so  as  to  afford  central  illumination,  or  it  may 
(condenser  and  all)  be  swung  laterally  up,  say  to  an 
angle  of  40  or  50  degrees  from  the  axis;  and  it  further 
remains  to  say  that  either  of  these  cheap  objectives  are 
real  good,  honest  glasses  for  the  money. 


186  HOW   TO   SEE   WITH  THE   MICROSCOPE. 


SUNLIGHT. 

In  the  study  of  very  minute  and  delicate  structures 
requiring-  the  utmost  separating  or  resolving  power  of 
the  objective,  remarkable  effects  are  to  be  secured  by 
condensing  sunlight  on  top  of  the  object  by  means  of 
the  concave  mirror,  the  object  being  mounted  with  a 
cover  in  the  usual  way.  The  objective  used  should  of 
course  have  wide  aperture.  The  mirror  being  posed 
slightly  above  the  level  of  the  stage,  the  sunlight  is 
thrown  on  the  surface  of  the  cover,  and  making  a  very 
acute  angle  therewith.  Although  not  absolutely  neces- 
sary for  this  purpose,  those  stands  furnished  with  swing- 
ing sub-stages,  allowing  the  mirror  to  rise  above  the 
level  of  the  stage,  are  extremely  handy  and  convenient. 
By  the  employment  of  this  illumination  in  conjunction 
with  object-glasses  of  wide  angles,  the  most  difficult 
diatoms,  such  as  amphipleurapellucida,f?*ustulia  saxon-ica, 
etc.,  are  easily  and  forcibly  displayed.  The  advantages- 
attending  the  use  of  monochromatic  sunlight,  as  ob- 
tained by  the  intervention  of  the  cupro-ammonia  cell, 
or  a  plate  of  blue  glass,  have  long  been  known.  Thi& 
illumination  is  procured  most  easily  as  follows:  Cut 
with  a  diamond,  or  the  point  of  a  file,  a  small  piece  of 
the  blue  glass  roughly  to  fit  the  cap  of  the  eye-piece, 
p.o  that  when  the  cap  is  restored  to  its  place  the  blue 
glass  shall  be  between  the  eye  and  the  eye-lens  of  the 
eye-piece,  and  the  light  is  thus  modified  before  it  reaches 
the  eye.  This  is  the  handiest  method  of  obtaining  mo- 


ARTIFICIAL   LIGHT.  1ST 

nochromatic  illumination  we  have  ever  tried,  and  the- 
resolutions  are  quite  as  strong1  and  effective  as  when  the 
cupro-ammonia  cell  is  used  in  the  usual  manner.  In 
working  with  sunlight  by  either  of  the  methods  de- 
scribed, care  should  be  taken  to  exclude  the  full  strength 
of  the  solar  beam ;  that  is,  if  the  sun  be  clear  and  bright. 
Too  much  light,  supposing  the  manipulations  are  tolera- 
bly well  attended  to,  will  be  manifest  by  the  appearance 
of  a  multitude  of  diffraction  lines,  and  these  as  a  rule 
may  be  recognized  by  their  extending  beyond  the  ob- 
ject observed.  Under  very  high  amplifications,  involv- 
ing the  use  of  powerful  eye-pieces,  we  can  of  course- 
help  ourselves  to  a  little  more  of  the  solar  beam.  When 
the  sun  is  very  clear,  the  beam  being  condensed  on  the 
top  of  the  cover,  as  above  described,  there  is  danger 
sometimes,  if  the  object  be  balsam  mounted,  of  the  heat 
starting  the  balsam.  In  this  way  we  once  ruined  a 
Moller  probbe  plate.  A  very  little  attention  will,  how- 
ever, provide  against  accidents  of  this  nature. 

ARTIFICIAL  LIGHT. 

For  the  ordinary  purposes  of  the  microscopist  the  St. 
Germain  or  German  Student's  Lamp,  0.  A.  Kleemann's 
patent,  or  a  similar  lamp  made  by  the  Cleveland  Com- 
pany, will  be  found  quite  satisfactory.  This  style  of 
lamp  is  too  well  known  to  require  any  extended  descrip- 
tion. The  flame  is  bright,  clear  and  intense,  and  its 
height  can  be  changed  at  will.  It  is  easily  kept  in 
order,  and  has  the  advantage,  too,  of  being  well  adapted 
for  ordinary  household  purposes.  The  breakage  of 


188  HOW   TO   SEE   WITH   THE   MICROSCOPE. 

•chimneys  has  been  a  serious  objection  to  its  use ;  a  brand 
of  chimney  known  in  Cleveland  as  the  "  Crown"  (each 
chimney  having  a  crown  ground  in  the  glass)  seem  to 
be  very  free  from  breakage.  Non-combustible  wicks 
are  to  be  obtained,  fitting  the  Kleeman  lamp.  These 
are  clean  and  handy,  obviating  the  necessity  of  occa- 
sional cutting  and  trimming ;  but  to  our  mind  the  light 
is  not  so  intense,  and  therefore  we  prefer  to  use  the  old 
-style  of  wick.  These  lamps  burn  very  steadily,  and  are 
not  easily  affected  by  occasional  drafts,  and  this  is  a  strong 
recommendation  in  their  favor,  as  is  also  the  ease  with 
which  they  are  kept  in  order.  For  investigations  of 
^exceedingly  difficult  objects  the  circular  wick  is  not  so 
well  adapted,  and  recourse  must  be  had  to  lamps  carry- 
ing flat  wicks.  The  best  lamp  we  know  of,  of  the  lat- 
ter style  is  the  Mechanical  Lamp,  manufactured  in  New 
York  City.  The  lamp  stands  about  ten  inches  in  height. 
The  height  cannot  be  changed,  and  this  is  an  objection. 
It  burns  kerosene  oil,  without  any  chimney.  The  body 
contains  a  movement  which,  on  being  wound  like  a  clock, 
drives  a  blast  wheel,  and  thus  supplies  a  current  of  air 
at  the  point  of  combustion.  Although  there  is  a  peri- 
odicity noticeable  in  the  burning  of  this  lamp,  never- 
theless the  flame  is  very  steady,  is  very  intense,  and 
superior  to  gas.  Like  the  St.  Germain,  this  lamp  is 
very  handy  to  have  in  the  house,  and  it  takes  but  little 
trouble  to  keep  it  in  order.  The  movement  should  be 
cleaned  once  a  year,  and  any  one  possessed  of  fair  me- 
chanical skill  will  be  competent  to  do  this.  While 
burning,  the  clock-work  makes  scarcely  any  noise.  An- 


ARTIFICIAL   LIGHT. 

other  form  of  this  lamp  has  the  movement  placed  in  the 
case  flatwise,  thus  allowing  the  flame  to  burn  within 
three  or  four  inches  of  the  table.  The  lamp  is  thus  ren- 
dered very  handy  for  use  when  direct  light  is  wanted. 

The  author  has  found,  as  a  result  of  thousands  of  ex- 
periments, that  the  very  best  artificial  light  for  the  pur- 
pose of  the  microscopist  is  only  to  be  had  from  a  small 
but  very  intense  flame.  The  smaller  the  flame  the  better, 
owing  to  the  fact  that  there  is  less  light  diffused.  We 
therefore  use  and  strongly  recommend  the  smallest  ker- 
osene hand-lamp  procurable,  and  fitted  with  a  well-be- 
haved burner  of  the  smallest  capacity.  If  possible  let 
the  lamp  bowl  be  so  low  that  the  flame  will  be,  say  three 
or  four  inehes  only  above  the  table,  thus  adapting  the 
lamp  for  use  by  direct  light.  On  other  occasions  the 
lamp  can  be  supported  in  a  more  elevated  position. 
With  a  little  lamp  of  this  description,  in  proper  order r 
all  the  most  difficult  tests  known  to  the  microscopist 
can  be  well  displayed,  provided,  obviously,  that  the  ob- 
jective, etc.,  shall  be  competent  for  the  work.  It  is  of 
importance,  when  any  lamp  provided  with  a  chimney  is 
to  be  used,  that  the  latter  be  kept  scrupulously  clean,, 
especially  from  a  whitish  film  that  forms  on  the  interior. 
A  chimney  may  appear  to  be  perfectly  clean  while  cold, 
but  when  heated  the  aforesaid  film  can  be  detected,  and 
should  be  removed,  if  delicate  observations  are  in  hand, 
in  which  case  it  will  be  well,  too,  if  the  wick  be  three 
or  four  weeks  old,  to  remove  the  same  and  substitute  a 
fresh  one.  Even  in  the  case  of  the  small  pattern  of 
lamp  recommended  there  will  be  no  occasion  to  force 


190  HOW   TO    SEE   WITH   THE   MICROSCOPE. 

the  combustion  to  the  fullest  extent  such  a  burner  will 
^afford.  A  flame  with  the  lamp  burning'  at  one-half  its 
capacity  will  be  amply  sufficient,  and  even  this  would 
be  too  much  for  the  proper  display  of  some  of  the  most 
•difficult  tests. 

Attempts  have  been  made  to  modify  artificial  illumina- 
tion by  the  introduction  of  blue  tinted  chimneys,  white 
ground  illuminators,  etc.  We  have  patiently  tried  the 
^entire  list,  and  reject  them  all,  from  the  fact  that  there 
is  no  real  advantage  secured  by  their  adoption  which 
•cannot  be  obtained  in  a  simpler  way  without  them. 
The  neutral  tint  "  Light  Moderator,"  so  called,  is  a 
pleasant  thing  enough  for  use  with  moderate  amplifi- 
cations ;  yet  there  is  nothing  seen  with  it  that  cannot 
be  as  well  shown  without  it. 

The  blue  tinted  chimney  cuts  down  seriously  the  in- 
tensity of  the  lamp  illumination  to  an  extent  which  will 
defeat  the  resolution  of  any  severe  test,  while,  on  the 
•contrary,  any  and  all  work  with  the  lower  powers  can 
be  as  well  accomplished  without  its  aid. 

The  reader  has  thus  before  him  all  the  various  kinds 
of  illumination  we  use.  A  great  deal  of  the  profes- 
sional routine  of  work  not  requiring,  us  a  rule,  the  em- 
ployment of  the  highest  amplifications  (such  as  the 
examination  of  urinary  deposits,  malignant  growths, 
etc.,)  we  try  as  far  as  possible  to  accomplish  in  the  day 
time,  and  by  the  use  of  diffused  daylight.  If  the  sun 
happen  to  shine,  and  it  be  desirable  to  cross-question 
some  preliminary  examination  under  the  highest  pow- 
ers, we  generally  use  the  sunlight  condensed  on  the  top 


ARTIFICIAL    LIGHT.  191 

of  the  cover,  or  perhaps  v/ith  the  aid  of  the  bit  of  blue 
glass  in  eye-piece.  For  work  at  night  we  employ  at 
times  all  the  lamps  we  have  described.  Should  the 
routine  examinations  be  prolonged  into  the  evening,  we 
use  the  German  student's  lamp  for  preliminary  work, 
the  same  as  we  use  diffused  daylight  in  the  day  time. 
But  should  the  higher  amplifications  become  necessary, 
we  bring  the  mechanical  or  the  little  hand-lamp  into 
play.  The  German  student's  will  still  do  service  in  the 
lighting  up  generally  of  the  work-table  at  intervals. 
For  the  showing  of  such  objects  as  the  Nos.  18,  19,  and 
20  of  the  Moller  plate  by  lamplight,  of  course  the  little 
hand-lamp,  or  the  lower  model  mechanical  is  impera- 
tively employed,  especially  when  the  Wenham  "  reflex  " 
illuminator  is  selected. 

There  remains  yet  another  method  of  sunlight  illumina- 
tion which  will  be  found  useful  at  times.  I  refer  to  the 
use  of  the* 'reflex"  illuminator  with  direct  sun-light. 
In  this  case  the  solar  beam  can  be  received  through  a 
closed  window  (quite  a  boon  in  the  winter  season)  and 
reflected  from  the  plane  mirror.  This  illumination  is 
only  suitable  for  work  with  wide  apertures,  and  ever 
the  most  minute  objects,  and  the  mount  must  be  free 
from  surrounding  objects  of  a  coarse  character,  else, 
from  the  extremely  oblique  character  of  the  illumina- 
tion these  stronger  and  coarser  objects  will  project  their 
strong  shadows  across  the  field,  causing  nothing  but 
contusion  and  chaos.  With  the  genuine  form  of  the 
Wenham  "  reflex  "  an  epithelial  scale  would  hardly  be 
recognized  were  there  several  in  the  field.  The  princi- 


192  HOW   TO    SEE    WITH   THE    MICROSCOPE. 

pal  advantage  in  the  use  of  the  "  reflex  "  with  sunlight 
is  in  arriving  at  a  knowledge  of  surface  markings,  and 
for  this  purpose  it  is  indeed  very  valuable.  Thus  work- 
ing the  "  reflex  "  by  sunlight,  the  mirror  must  be  manip- 
ulated so  as  to  produce  the  same  effects  as  have  been 
described  by  moving  the  hand-lamp  and  conversely. 
The  mirror  may  be  substituted  for  the  hand-lamp  when 
working  in  the  evening,  but  the  most  favorable  results 
are  obtained  with  the  light  direct.  This  reflex  and  sun- 
light illumination  is  especially  desirable  when  one  wishes 
to  trace  out  structure  situated  in  one  particular  plane^ 
to  the  exclusion  of  that  lying  in  adjacent  planes.  In 
the  general  squabble  to  produce  the  so-called  penetra- 
tion, this  very  important  item  has  been  lost  sight  of. 

We  are  now  ready  to  consider  a  matter  which  has 
been  alluded  to  on  a  preceding  page.  It  has  been 
already  stated  that  the  maximum  performance  of  ad- 
justable objectives  can  only  be  secured  when  such  object- 
glasses  are  worked  at  the  point  of  their  maximum  aper- 
ture, and  that  this  point  is  by  no  means  a  fixture  but 
varies  with  different  objectives.  Every  observer  should 
then  ascertain  for  himself  as  to  the  proper  handling  of 
his  object-glasses  in  this  particular.  Methods  will  now 
be  given  which,  although  but  approximate,  are  suffi- 
ciently precise  for  the  use  of  the  practical  manipulator. 

For  the  purpose  of  testing  the  point  of  maximum 
aperture  for  object-glasses  having  apertures,  say  from 
40°  to  175°,  proceed  thus:  Place  the  objective  in  posi- 
tion on  any  good  stand  having  a  thin  stage  and  mirror 
attached  to  radial  arm.  Commence  by  focussing  any 


ARTIFICIAL   LIGHT.  193 

suitable  object  on  the  stage,  with  the  mirror  in  a  central 
position,  the  collar  of  the  objective  being  set  at  the  ex- 
tremity of  its  range.  Now,  by  degrees,  swing  the  radial 
bar  carrying  the  mirror,  meanwhile  adjusting  the  mirror 
so  as  to  secure  all  the  illumination  possible,  just  as  would 
occur  in  arranging  for  greater  obliquity  of  illumination, 
until  the  obliquity  of  the  light  becomes  as  great  as  the 
objective  will  bear;  i.  e.,  until  the  greatest  degree  of 
obliquity  has  been  obtained  that  will  secure  a  tolerably 
well-lighted  field.  Now  move  the  radial  bar  a  little, 
and  but  a  little  further  from  axis,  meeting  this  change 
by  the  proper  manipulation  of  the  mirror,  and  so  as 
still  to  secure  all  possible  light.  The  object  now  ought 
not  to  have  more  than  one-fourth  the  usual  illumination, 
but  should  nevertheless  be  distinctly  seen.  Next,  revolve 
the  collar  and  notice  the  effect.  If  you  get  less  and  less 
light  as  the  collar  is  turned  towards  the  other  extremity 
of  its  range,  it  would  show  that  it  was  already  at  the 
point  of  its  maximum  aperture ;  on  the  contrary,  should 
you  get  more  light,  it  will  be  apparent  that  the  aper- 
ture increases  as  the  collar  is  turned,  and  thus  turning 
the  collar  by  degrees,  move  also  the  radial  bar  still  fur- 
ther from  axis,  manipulating  the  mirror  as  before,  and 
to  the  same  end,  and  so  proceed  as  long  as  the  change 
of  the  collar  gives  more  light.  You  have  then,  by 
simple  inspection  of  the  position  of  the  adjustment,  a 
tolerable  idea  where  the  maximum  of  the  objective  is  to 
be  found.  Note  this :  Now  remove  the  object,  place  the 
stand  in  a  horizontal  position,  and,  without  changing 
the  adjustment  of  the  objective,  proceed  to  measure  its 

13  Microscopy. 


194  HOW  TO   SEE   WITH  THE   MICROSCOPE. 

angle  by  the  method  previously  given.  Note  again  the 
angle  obtained.  Next,  change  the  collar  adjustment  a 
division  or  two,  and  again  measure  the  aperture.  Com- 
paring results,  it  will  become  obvious  which  of  these 
two  positions  of  the  collar  corresponded  to  the  larger 
angle.  Should  the  latter  measure  prove  the  least,  it 
will  be  necessary  to  reverse  the  movement  of  the  col- 
lar, placing  it  a  division  or  two  from  the  previous  posi- 
tion but  in  the  reverse  direction,  and  by  a  few  measures 
of  this  kind,  which,  by  the  way,  are  quickly  accom- 
plished, the  point  in  the  collar  adjustment  correspond- 
ing to  the  maximum  aperture  on  the  glass  will  be  ascer- 
tained with  considerable  precision.  In  the  method  just 
described  the  primary  object  was  to  get  an  approximate 
idea  as  to  the  point  of  largest  aperture,  and  with  the 
least  outlay  of  time,  and  subsequently,  by  actual  trial, 
to  arrive  at  a  more  precise  determination.  The  whole 
process  involves  but  little  outlay  of  time,  ten  minutes 
being  quite  sufficient  for  the  purpose. 

With  objectives  of  high  balsam  angles  it  will  be  neces- 
sary to  employ  th6  genuine  Wenham  "  reflex  "  illumina- 
tor (angle  of  facet  26°).  With  this  instrument  proceed 
as  has  already  been  advised  until,  by  the  lateral  move- 
ment of  the  lamp  at  either  the  extremes,  right  or  left, 
the  illumination  commences  to  die  away,  the  field  being 
blue  or  red,  according  to  the  position  of  the  lamp.  It 
will  generally  be  a  saving  of  time  to  start  with  the 
collar  of  the  objective  at  "  closed."  Having  found  the 
best  position  for  the  lamp,  as  we  have  before  directed, 
move  it  still  a  little  further  laterally  until  the  field  of 


ARTIFICIAL   LIGHT.  195 

the  instrument  shall  only  be  illuminated  sufficiently 
to  enable  you  to  see  your  object  distinctly.  Now, 
keeping  things  thus,  revolve  the  collar,  and  notice  the 
effect  on  the  illumination,  and  thus,  as  in  the  case 
already  presented,  you  have  the  means  of  judging  as 
to  the  aperture  of  the  objective.  And  as  an  example 
I  now  relate  a  bit  of  experience  not  twenty-four  hours 
old :  We  have  just  had  in  hand  an  objective  claiming  to 
have  high  balsam  angle,  and  we  desire  to  know  some- 
thing about  it.  First,  we  look  to  its  working  distance 
and  find  that  it  will  work  through  covers  one-fiftieth  of 
an  inch  thick,  its  distance  is  therefore  ample.  Applying 
the  Wenham  "  reflex  "  we  test  as  to  aperture,  and  pre- 
cisely as  has  been  above  described,  thereby  learning 
that  its  greatest  angle  occurs  when  the  systems  are  at 
"closed."  We  find,  too,  that  as  the  collar  is  revolved 
towards  the  "  open  point,"  the  angle  goes  down  rapidly. 
We  therefore  conclude  that  to  work  this  glass  at  its 
maximum  performance  it  will  be  necessary  to  use  covers 
thick  enough  to  cause  the  objective  to  "correct"  at  or 
near  "  closed.'5  It  will  take  but  a  moment  to  try  the 
actual  experiment,  aud  to  see  if  theory  holds  good  in 
practice.  For  this 'purpose  we  place  the  "reflex"  in 
position  and  the  No.  20  of  the  balsam  Moller  plate  on 
the  stage,  making  immersion  contact  with  water.  Next, 
we  attempt  the  resolution  of  the  shell,  and  with  the 
best  manipulations  at  our  command  succeed  in  getting 
but  a  tolerable  show  of  the  striae.  I  have  the  blue  field 
in  hand,  with  the  lamp  at  the  extremest  point  to  the 
left:  the  best  display  being  thus  obtained,  as  the  lamp 


196  HOW   TO    SEE   WITH   THE    MICROSCOPE. 

was  thus  shoved  to  the  left  the  definition  was  improved, 
but  we  were  compelled  to  desist  from  this  movement 
owing  to  the  loss  of  light,  and  were  therefore  content 
with  the  lamp  as  far  to  the  left  as  was  possible  without 
sacrifice  of  the  illumination.  Of  course  the  objective 
was  adjusted  with  all  possible  care,  the  collar  standing 
within  three  divisions  from  "  open  point." 

We  now  carefully  raise  the  objective,  and  removing 
the  water  with  a  bit  of  blotting  paper,  we  substitute  a 
drop  of  glycerine,  focussing  and  adjusting  the  glass 
again  with  the  glycerine  intermedium ;  the  glass  now  ad- 
justs at  nearly  closed,  the  collar  having  made  nearly  two 
full  revolutions  from  its  former  position.  It  is  further 
obvious  that  we  have  now  more  light  generally;  we 
can,  too,  move  the  lamp  to  a  greater  distance  right  or 
left  without  loss  of  illumination.  In  fact,  things  in 
the  tube  have  a  sunshine  appearance  that  is  very  accept- 
able. We  now  attempt  again  the  resolution  of  the 
same  shell,  using  the  blue  field  as  before.  Finding  that 
the  lamp  will  bear  to  be  shoved  further  to  the  left  than 
before.  And  now,  even  before  arriving  at  the  limit  of 
light,  i.  e.,  the  lamp  not  so  far  to  the  left  as  we  might 
place  it,  we  are  rewarded  by  a  splendid  display  of  the 
transverse  striae,  this,  too,  with  illumination,  I  was 
going  to  say  in  excess,  at  all  events  enough  to  allow  the 
use  of  the  one-halt  and  the  one-fourth  solid  eye-pieces. 

We  have  thus  described  this  experience  taken  from 
our  private  practice,  giving  the  actual  results  obtained. 
Well,  now,  suppose  that  with  the  Wenham  reflex  the 
experiment  had  turned  out  a  total  failure;  i.  e.,  that  we 


ARTIFICIAL    LIGHT.  197 

could  get  no  light  through  the  objective,  showing  that 
in  this  case  the  accessory  was  a  reflex  and  no  mistake ; 
or,  suppose  that  our  best  efforts  were  only  rewarded  by 
a  dim  view  of  the  diatom  seen  doubled  up  endwise  amid 
a  plexus  of  indeterminate  undefinable  diffraction  lines, 
the  entire  field  miserably  illuminated,  of  a  muggy, 
smoky,  dingy  yellow,  as  if  a  piece  of  yellow  flannel 
had  been  used  in  place  of  the  lamp,  and  that  we  could 
only  get  this  much  in  just  one  solitary  position  of  the 
lamp ;  then  the  experimsnt  is  quite  as  interesting,  quite 
as  valuable,  and  if  made  in  due  time  will  amply  repay 
its  cost. 

As  a  matter  of  course,  the  lower  the  balsam  aperture 
the  lower  will  be  the  grade  of  its  work  with  the  "  re- 
flex ;"  nevertheless,  the  point  of  maximum  performance 
can  be  ascertained  by  the  method  above  given,  and  in 
the  testing  of  object-glasses  I  make  it  a  point  to  look 
after  the  balsam  angle  and  the  point  of  maximum  aper- 
ture at  the  same  sitting,  the  only  additional  trouble 
involved  being  the  change  in  the  thickness  of  cover,  or, 
as  in  the  instance  named,  substituting  glycerine  in  place 
of  water. 

We  have  entered  into  these  details,  feeling  assured 
that  the  facts  are  worth  knowing,  and  that  many  there 
be  who  have  not  given  these  things  due  attention.  Of 
those  who  have  visited  us,  eight  out  of  ten  saw  the  work- 
ing of  the  "reflex"  lor  the  first  time,  while  without 
exception  all  have  seemed  greatly  pleased  and  interested 
with  such  comparative  experiments  as  we  have  just  de- 
scribed. Let  the  reader  rest  a  moment  here  and  I  will 
relate  a  little  incident : 


198  HOW  TO   SEE   WITH  THE   MICROSCOPE. 

Not  long  since  I  was  honored  with  a  call  from  a  gen- 
tleman who  had  put  himself  to  some  little  trouble  in 
visiting  Cleveland.  Said  he:  "I  have  been  for  some 
time  desirous  of  visiting  you ;  I  have  read  all  your  ar- 
ticles in  the  journals,  and  have  been  permitted  to  read 

your  letters  to  our  mutual  friend, .     I  want 

to  know  something  more  about  the  "  balsam  angle " 
business;  ditto,  about  the  "  180°";  I  confess  these  ex- 
treme apertures  seem  to  me  "  impossible";  and  then, 
again,  we  have  high  authority  that  the  true  aperture  of 
any  object-glass  cannot  exceed  120°  and  the  assertion  is 
fortified  with  reasoning  that  I  cannot  well  dodge.  I 
have  brought  with  me  an  excellent  glass  purporting  to 
have  corrected  angle  up  to  140°,  and  would  like  to  have 
some  comparisons  made  with  your  own.  I  am  after  the 
facts,  and  have  no  personal  bias  in  any  direction,"  etc., 
etc.  He  also  went  on  to  state  that  Mr.  Wenham  had 
expressly  asserted  that  direct  light  could  be  obtained 
with  the  "  reflex."  At  his  suggestion  I  showed  him 
the  No.  18  of  the  balsam  Moller  probbe  plate  illumina- 
ted with  the  genuine  "  reflex."  The  field  was  brilliantly 
lighted  with  just  enough  of  the  blue  in  to  take  off  the 
intensity  of  the  glare.  The  shell  appeared  without  sen- 
sible distortion,  edges  sharp  and  clean,  and  with  a  full 
stand  of  lines  from  end  to  end.  Revolving  the  stage  so 
as  to  place  the  saxonica  in  a  diagonal  position,  we  had 
little  difficulty  in  obtaining  simultaneous  views  of  both 
transverse  and  longitudinal  strise,  thus  cutting  the  valve 
into  checks  or  squares.  The  same  little  hand-lamp  was 
used,  and  we  had  nice  shows  with  eye-pieces  up  to  the 
one-fourth  inch. 


ARTIFICIAL    LIGHT.  199 

My  visitor  was- delighted,  nor  did  he  attempt  to  con- 
ceal his  delight.  "  Now,"  said  he,  "just  keep  all  things 
just  as  they  are,  but  take  off  your  glass  and  put  on 
mine."  The  same  was  accordingly  done,  and  the  result 
was  that  we  could  not  see  the  diatom  at  all,  nor  could 
we,  by  the  best  possible  manipulation  of  the  Limp,  see 
it  well  enough  to  recognize  it.  I  suggested  the  possi- 
bility that  the  glass  might  not  be  truly  centered,  and 
thus  to  some  extent  be  defeated.  Attention  was  there- 
fore given  to  this,  but  without  avail.  My  friend's  ob- 
jective positively  refused  to  have  anything  to  do  with 
the  reflex  illuminator. 

Now,  I  have  found,  by  countless  experiments,  that  of 
two  objectives,  the  one  working  well  with  the  genuine 
"  reflex,"  and  another  refusing  to  so  work  at  all,  the 
former  will  be  far  the  superior  glass  for  any  and  all 
work;  a  fact  which,  after  a  little  subsequent  experi- 
ment my  visitor  was  not  slow  to  accept.  I  am  of  course 
referring  to  objectives  generally  known  under  the  ap- 
pellation of  "  high  powers." 

Thus  it  will  be  seen  that  the  Wenham  "  reflex  "  is  for 
any  of  these  purposes  quite  a  handy  and  effective  little 
instrument,  and  ought  to  have  its  place  in  the  accessory 
box  of  every  microscopist.  It  will  serve,  too,  in  its 
legitimate  capacity  as  designed  by  its  inventor,  i.  e»  as 
a  "  dark  ground  illuminator;"  but  herein  will  be  found 
its  least  value.  To  return  directly  to  our  subject:  I 
cannot  too  strongly  recommend  that  every  one  inter- 
ested in  microscopical  work  requiring  the  employment 
of  high  amplifications  with  fine  defining  power,  should 


200  HOW   TO   SEE   WITH   THE   MICROSCOPE. 

study  their  objectives,  and  if  for  the  sake  of  practice 
only,  those  of  their  friends  to  which  they  can  have 
access.  There  is  no  time  lost  in  this  occupation ;  on 
the  other  hand,  it  will  usually  result  in  economy  of 
time.  For  instance,  if  your  glass  totally  refuses  to  asso- 
ciate with  the  genuine  "  reflex,"  you  are  hereby  informed 
that  such  a  glass  is  totally  unfit  for  any  such  purpose 
as  resolving  the  last  numbers  of  the  Moller  probbe  plate, 
or  for  any  kind  of  duty  requiring  the  recognition  of 
lines  as  close  as  80,000  to  the  inch.  Thus,  by  the  method 
described  you  can,  in  less  than  ten  or  fifteen  minutes 
time,  settle  definitely  any  such  question  as  to  the  capacity 
of  your  object-glass. 

This  matter  is  suggestive,  and  with  the  reader's  per- 
mission I  desire  to  "  switch  off  on  a  side  track  "  again, 
for  we  have  "  an  ax  to  grind."  We  often,  yea,  almost 
every  day,  hear  those  who  regard  the  study  of  objectives 
as  one  worth  attention,  roundly  condemned  by  workers 
in  natural  history,  biology,  etc.  The  former  are  said  to 
be  "  only  diatom  crackers,"  wlio  do  nothing  but  fool 
away  their  time  over  difficult  diatoms,  and  are  said  to 
have  angular  aperture  "  on  the  brain."  Now,  reader, 
when  you  shall  be  permitted  to  peep  behind  the  curtain 
as  often  as  I  have  had  the  chance  in  the  past  (which,  by 
the  way,  I  have  improved),  you  will  find  that  the  very 
gentlemen  who  make  all  this  hue  and  cry  are  the  very 
ones  who  have  been  and  still  are  "  fooling  away"  their 
time.  You  will  find,  as  a  rule,  that  each  and  every  one 
of  them  have  their  little  cabinet  of  "  difficult  tests," 
over  which  they  spend  (sub  rosa)  night  after  night  in 


ARTIFICIAL    LIGHT.  201 

an  absurd  attempt  to  display  the  hateful  markings ;  an 
attempt,  too,  as  futile  and  puny  as  that  of  the  child  who 
cries  for  a  piece  of  the  moon.  And  why?  Simply  be- 
cause the  object-glass  employed  is  not  suited  to  the  work 
in  hand.  Nor  is  the  picture  overdrawn,  as  more  than 
one  lady  can  attest,  or  the  "  looker  on  in  Venice " 
vouch  for. 

To  all  such,  to  all  who  value  the  microscope  as  an  aid 
to  scientific  investigation,  let  me  urge  the  importance 
of  studying  well  the  nature,  capacity  and  capabilities 
of  the  objective,  and  to  this  end,  and  in  the  special  line 
we  have  been  discussing,  the  Wenham  "  reflex"  will 
prove  itself  a  valuable  and  important  accessory,  and  a 
time  saver  of  the  very  first  water. 


CHAPTER  VI. 

CHOICE   OF   OBJECTIVES   FOR  REGULAR   WORK. 

Practically,  for  the  past  four  years,  we  have  confined 
ourselves  to  the  use  of  four  object-glasses,  namely,  an 
inch  or  two-thirds  inch  of  45°  or  50°.  A  one-half  inch 
of  38°.  A  one-sixth  immersion,  balsam  angle  ranging 
from,  say  87°  to  95°,  according  to  the  position  of  its 
collar,  and  a  one-tenth  immersion  having  a  constant 
angle  of  100°.  Of  the  last  two  glasses,  the  one-sixth 
has  a  working  distance  of  one-fiftieth  of  an  inch.  The 
one-tenth  will  work  readily  through  covers  one-one- 
hundredth  of  an  inch  thick. 

The  orthodox  theory  has  been,  and  I  suppose  still  is, 
that  each  worker  ought  to  select  his  stand,  objectives,, 
accessories,  etc.,  with  special  reference  to  the  particular 
line  of  investigations  he  may  elect  to  pursue;  and  since, 
as  before  intimated,  there  may  be  more  or  less  force 
attached  to  such  a  platform,  I  neither  accept  it  nor  reject 
it;  nor  am  I  "  on  the  fence,"  halting  between  two  con- 
flicting opinions.  Without  going  into  any  special  dis- 
cussion of  the  pros  or  cons,  we  will  proceed  to  state  the 
character  of  the  work  in  which  we  have  been  engaged, 
accompanied  with  a  recital  of  the  special  methods,  etc., 
employed. 

First;  we  use  the  microscope  constantly  from  January 
to  December  in  examination  of  urinary  deposits,  and 
for  the  study  and  detection  of  malignant  growths.  In 


CHOICE    OF   OBJECTIVES    FOE    REGULAR   WORK.       203 

conjunction  therewith  the  aid  of  medical  chemistry  is 
constantly  sought,  especially  in  the  diagnosis  of  renal 
diseases.  Work  of  this  description  is  continually  on 
the  tapis  "  all  the  year  round."  In  addition  to  this  we 
use  the  instrument  as  a  necessary  aid  in  our  daily  lec- 
tures, and  for  the  private  instruction  of  students  at  the 
college  on  matters  pertaining  to  our  Chair  of  Histology 
and  Microscopy.  Besides  these  duties  we  have  more  or 
less  private  instruction  entirely  outside  of  the  college 
to  attend  to.  The  range  of  work  then  to  be  accom- 
plished is  by  no  means  a  narrow  one,  and  anything  in 
the  way  of  instrumentation  that  would  assist  either 
teacher  or  pupil  will  find  at  all  times  in  my  laboratory 
a  ready  market. 

We  thus  state  the  character  of  the  work  we  have  in 
hand,  and  also  the  instrumentation  employed  for  its  ac- 
complishment; perhaps  a  leaf  or  two  from  our  daily 
practice  may  prove  acceptable,  and  with  this  hope  we 
proceed : 

We  have  said  that  a  large  amount  of  our  work  is 
over  urinary  deposits.  For  this  purpose  we  use  the 
"  histological "  stand  of  Mr.  Zentmayer,  the  tube  short 
and  the  stage  level.  Nine  physicians  out  of  ten  engaged 
in  similar  examinations  use  their  instruments  in  an  in- 
clined position,  covering  their  preliminary  mounts, 
absorbing  the  superfluous  moisture  with  a  bit  of  blot- 
ting paper,  employing,  too,  an  objective  as  high  as  the 
one-fourth,  or  perhaps  higher.  Now  nine-tenths  of  all 
work  of  this  description  can  be  accomplished  with  a  wide 
angled  inch  or  two-thirds,  and  by  keeping  the  tube  short 


204  HOW   TO   SEE    WITH   THE   MICROSCOPE. 

and  the  stage  level  there  will  be  found,  in  ninety-live 
cases  out  of  the  hundred  no  necessity  for  covering  the 
mount.  I  simply  place  on  a  clean  glass  slide  a  drop  of 
the  specimen  to  be  examined  and,  without  covering  it  at 
nil,  place  the  same  on  the  stage,  the  spring  clips  being 
turned  back  out  of  the  way,  for  even  these  are  a  draw- 
back to  rapid  work.  It  will  be  often  necessary  to  use 
re-agents,  and  to  this  end  the  long  working  distance 
.affords  every  facility.  With  this  two-thirds  or  the  inch  I 
ivm  enabled,  by  eye-piecing,  to  get  nice  definition  up,  say 
to  200  or  250  diameters.  Here  we  have  &  practical  ad- 
vantage arising  from  the  use  of  a  high -angled  glass,  and 
one  of  the  greatest  value.  In  thus  being  able  to  dispense 
with  the  use  of  covers  a  wonderful  saving  of  time  is 
accomplished;  the  objective,  too,  is  far  enough  out  of 
the  way,  so  that  it  does  not  become  clouded  by  the 
evaporation,  nor  injured  by  the  fumes  of  the  re-agents. 
Any  desirable  change  in  amplification  that  can  ordina- 
rily occur  is  furnished  instantly  by  changing  the  e}'e- 
piece.  And  here  let  me  say  that  the  oculars  should  slip 
in  and  out  of  the  tube  just  as  easily  as  possible  without 
decentering  the  object  viewed.  A  tight  fitting  eye-piece 
is  an  abomination  of  the  first  order;  any  ocular  of  mine 
will  drop  out  of  the  tube  instantly  by  tipping  the  stand 
•"  upside  down."  Now  the  advantage  of  the  short  tube 
is  this:  You  are  enabled  to  work  over  a  table  of  the 
ordinary  height,  and  to  view  your  object  comfortably, 
at  the  same  time  the  table  forms  a  very  acceptable  rest 
for  the  forearm ;  on  the  other  hand,  by  keeping  the  tube 
its  standard  length  one  must  use  a  lower  table,  and  the 


CHOICE    OF   OBJECTIVES   FOR    REGULAR   WORK.       205 

rest  for  the  arms  can  no  longer  be  obtained  unless  some 
recourse  be  had  to  blocking  up  by  books  and  the  like. 

Now  in  an  examination  involving  three  or  four  hours' 
time,  it  is  quite  possible  that  it  may  be  desirable  to  sub- 
stitute in  the  place  of  the  two-thirds  a  glass  that  will 
give  higher  amplifications.  In  this  case  the  two-third 
would  be  removed'and  the  one-sixth  called  on  to  take  its 
place.  Now  I  have  previously  found  out  that  the  one- 
sixth  has  maximum  performance  when  worked  over  the 
thickest  covers.  These  I  have  already  selected  and 
placed  in  a  little  box  by  themselves,  one  of  which  is 
carefully  cleaned  and  placed  over  my  object,  the  micro- 
scope tube  pulled  out  to  the  standard  length,  the  instru- 
ment inclined  to  a  suitable  angle,  and  thus  the  exam- 
ination goes  on.  In  extreme  cases  the  one-tenth  would 
be  again  substituted  for  the  one-sixth.  With  this  glass, 
having  as  it  has,  maximum  performance  at  any  point  »f 
its  cover  adjustment,  there  need  be  no  particular  care 
exercised  as  to  the  selection  of  the  cover,  further  than 
to  see  that  the  same  be  thin  enough. 

It  will  be  noticed  that  with  the  employment  of  the 
immersions  the  tube  should  be  restored  to  the  standard 
length.  This  is  an  important  item,  and  should  never  be 
omitted  when  there  is  nice  work  in  hand.  These  wide- 
apertured  glasses  are  especially  intended  by  the  optician 
to  be  worked  with  tubes  of  standard  lengths.  The 
range  of  collar  adjustment,  too,  is  in  many  instances 
arranged  conformably  thereto. 

In  observations  over  urinary  deposits  I  contrive  to  do 
a  great  deal  of  work  with  the  one-half  inch.  Of  the 


206  HOW  TO   SEE   WITH  THE    MICROSCOPE. 

two,  the  two-thirds  or  the  wide-angled  inch  is  much  the 
superior  glass ;  but  I  value  these  so  highly  that  I  dread 
to  use  them  over  the  fumes  of  chemicals.  Hence  I  make 
the  cheaper  glass  do  all  that  I  possibly  can,  and  in  this 
kind  of  a  way  the  glass  is  really  useful  to  me. 

It  will  doubtless  be  observed  that  in  changing  from 
the  inch  or  two-thirds  to  the  one-sixth  or  one-tenth  I 
make  a  pretty  big  jump.  This  has  often  occurred  to 
me,  and  has  led  to  the  trial  of  several  intermediate 
powers,  resulting  in  every  instance  in  my  going  back  to 
first  principles;  we  are  still  of  the  notion  that  a  No.  1, 
four-tenths,  or  say  three-tenths  of  the  very  highest 
aperture  possible,  would  be  a  valuable  glass  in  the  lab- 
oratory, especially  in  such  examinations  as  those  of 
urinary  deposits  or  histological  work  generally,  and  we 
hope  before  long  to  own  just  such  a  glass,  which,  if  a 
success,  shall  not  be  allowed  to  <k  hide  its  light  under  a 
bushel." 

In  the  examination  of  malignant  growths,  and  in  the 
study  of  minute  pathology  generally,  the  aforesaid  pro- 
gramme is  somewhat  modified.  In  this  line  one  can 
very  often  make  entire  and  satisfactoiy  examinations 
with  a  "  medium  power  "  glass;  therefore,  and  princi- 
pally for  the  sake  of  convenience,  I  have  in  reserve  a 
dry  one-fourth  of  100°.  This  objective  (the  dry  front 
to  my  one-sixth)  will  give  me  nice,  clean  and  reliable 
views  under  ampliations,  say  from  200  to  600  or  700 
diameters.  The  mechanical  working  of  its  screw  collar- 
is  smooth  and  efficient,  and  the  glass  responds  promptly 
to  any  change  thereof.  Hence  it  has  worked  its  way  into 


CHOICE   OF   OBJECTIVES    FOR    REGULAR    WORK.       207 

favor  and  use.  It  is  not  a  strictly  necessary  objective  in 
the  laboratory,  for  the  one-sixth  will  of  course  do  all 
that  can  be  expected  of  the  one-fourth,  and  a  great  deal 
more  besides.  The  one-fourth  is  used  precisely  under 
the  circumstances  stated ;  when  there  is  work  on  hand 
likely  to  call  for  the  shifting  of  objectives,  the  one- 
fourth  is  very  likely  to  remain  in  its  box.  Thus  it  will 
be  seen  that  my  "  working  '"  battery  of  objectives  is  not 
numerically  very  formidable,  and  I  may  add,  not  very 
expensive. 

Having  thus  stated  my  own  course  in  the  way  of  se- 
lecting objectives  for  my  particular  work,  let  us  now 
turn  our  attention  to  a  condition  of  things  which  is 
occurring  everyday,  to  wit:  A  young  physician  just 
graduated  wishes  to  use  the  microscope  in  his  (expected) 
practice.  It  is  important  to  him  that  the  investment 
in  an  outfit  be  made  with  reference  to  the  strictest  econ- 
omy. The  author  has  in  the  past,  and  is  now,  receiving 
many  letters  of  this  sort,  to  one  of  which  he  replied 
but  a  day  or  two  ago  substantially  as  follows: 

The  fundamental  idea  in  purchasing  an  outfit  ought 
to  be  this:  To  buy  nothing  with  the  view  of  replacing 
it  bye-and-bye  for  something  better  of  the  sort,  with  an 
indefinite  hope  that  the  original  article  can  be  disposed 
of  at  no  great  loss.  On  the  contrary,  let  every  purchase 
be  made  and  every  detail  carefully  selected  with  the  in- 
tention of  avoiding  any  future  substitution  or  exchange. 
Any  departure  from  this  fundamental  law  will  be  at  the 
sacrifice  of  strict  economy ;  therefore  we  reply  to  our 
•correspondent  in"  this  tenor,  recommending  that  he  pur- 


208  HOW   TO    SEE    WITH   THE    MICROSCOPE. 

chase  a  one-inch  like  those  furnished  by  Mr.  Gundlach 
or  the  Messrs.  Beck ;  and  for  a  high  power  select  the 
professional  one-fourth  of  the  Messrs.  Spencer  &  Sons, 
or  its  equivalent  by  any  other  maker.  With  these  twa 
glasses  the  physician  can  accomplish  seven-tenths  of  any 
and  all  work  he  may  be  professionally  called  on  for. 
Either  one-inch  named  is  a  good  reliable  glass,  giving, 
when  working  with  suitable  oculars,  very  good  shows- 
indeed,  and  infinitely  better  than  the  imported  French 
triplet,  while  the  cost  is  but  very  slightly  enhanced. 
We  recommend  a  one-fourth  similar  to  the  Spencer  pro- 
fessional, because,  having  used  one  ourselves,  we  can 
speak  "  by  the  card."  One  very  strong  reason  is,  that 
the  adjusting  collar  mechanism  (although  moving  the 
front  lens)  is  very  smooth  and  satisfactory  in  its  work- 
ing. A  still  more  important  reason  is  that  these  glasses 
respond  nicely  to  any  movement  of  the  collar,  and  they 
are,  too,  well  corrected  throughout  the  range  of  their 
aperture.  The  purchaser  is  thus  thrown  early  in  con- 
tact with  an  adjusting  objective,  and  hence  by  his  daily 
practice  will  he  become  more  and  more  skilled  in  it& 
use. 

The  author  desires  the  reader  to  make  a  special  point 
of  this :  Many  there  be  who,  having  bought  adjustable 
objectives  of  poor  quality,  and  having  discovered  "prac- 
tically "  that  the  position  of  the  collar  adjustment  with 
such  glasses  hardly  affects  in  any  way  their  efficiency  of 
performance,  not  only  let  them  alone  for  the  future,  but 
settle  down  strong  in  the  faith  that  collar  adjustment 
don't  amount  to  much,  and  that  the  "  handling"  of  aD 


CHOICE    OF   OBJECTIVES    FOR    REGULAR    WORK.       201) 

objective  sometimes  read  about  is  simply  a  myth.  Here 
is  another  instance  where  the  French  proverb  fits  to  a 
charm.  The  fundamental  error  having  been  committed, 
the  evil  consequences  are  sure  to  follow  suit. 

Now  in  the  course  of  a  year  or  two,  our  correspond- 
ent having  meanwhile  obtained  some  considerable  know- 
ledge of  the  microscope,  and  being  in  a  position  to 
make  a  further  investment,  he  has  simply  to  purchase  a 
first  class  inch  (or  two-thirds)  of  45°,  the  old  inch  will 
still  do  good  service  either  as  a  "hack"  lens  for  his 
rough  preliminary  work,  or  it  can  be  made  to  do  yeo- 
man's duty  as  a  condenser,  as  has  already  been  referred 
to,  It  will,  in  very  fact,  be  just  as  much  needed  as 
before ;  there  will  be  no  thought  or  occasion  for  its  sale 
or  exchange. 

It  will  probably  happen,  too,  that  in  a  little  while 
the  one-fourth  will  be  supplemented  by  the  addition 
of  a  one-sixth  or  one-tenth  of  high  balsam  angle.  In 
this  case  the  great  advantage  derived  from  the  previous 
use  of  the  one-fourth  will  at  once  be  made  manifest. 
Our  correspondent  will  be  enabled  to  work  the  new 
glass  with  tolerable  satisfaction  at  sight,  improving 
daily  as  he  continues  its  use;  and  if  so  be  that  he  can 
get  a  few  words  of  instruction  from  some  acknowledged 
expert,  they  will  be  readily  understood  and  appreciated. 
And  here,  again,  note  that  the  one-fourth  does  not  even 
now  become  a  superannuated,  worn  out  objective,  to  be 
sold  at  the  first  chance  to  the  highest  bidder.  On  the 
other  hand,  it  will  continue  to  be  used  generally  for  a 
considerable  time  while  experience  with  the  last  pur- 


210  HOW   TO   SEE   WITH   THE   MICROSCOPE. 

chase  is  being  gained.  In  short,  it  will  remain  "  a 
good  thing  to  have  in  the  house  "  until  some  genius  like 
Spencer  or  Tolles  shall  generally  upset  all  our  arrange- 
ments by  some  master  stroke  of  advancement.  There 
is  no  defence  possible  to  provide  against  such  an  emer- 
gency. 

We  desire  here  to  say  that  our  remarks  as  to  object- 
ives also  apply  as  to  the  purchase  of  stands.  The  man 
who  purchases  a  stand  "just  for  a  year  or  two,"  as  very 
many  have  done,  and  are  still  doing,  does  so  at  a  sacrifice 
•of  true  economy. 

But  we  have  correspondents  of  another  class.  Says 
one,  "the  inch  you  name  costs  $7.00;  the  one-fourth 
inch,  $20.00,  making  $27.00;  now  I  can't,  for  stand  and 
objectives,  spend  but  $45.00,  or  at  the  very  most,  $50.00; 
and  then  there  is  a  sub-stage  arrangement  recommended ; 
also,  an  extra  eye-piece  or  two.  What  shall  I  do?  This 
is  all  the  money  I  have  got,  and  I  have  to  take  the 
clothes  off  my  back  to  expend  this  much." 

Now  to  all  such,  and  there  are  many  of  them,  we 
reply,  make  a  "  virtue  of  necessity."  The  situation  is 
unfortunate,  but,  as  you  say,  it  cannot  be  helped.  If, 
by  waiting  a  short  time,  things  can  be  improved,  then 
you  had  better  postpone  your  purchase.  If  to  the  con- 
trary, then  invest  as  best  you  may  under  the  circum- 
stances. Keep  this  in  mind:  Of  the  two  evils,  sacrifice 
the  stand  rather  than  the  objective  ;  the  latter  MUST  be 
maintained  up  to  the  standard  given.  You  might  pos- 
sibly substitute,  in  place  of  the  one-fourth,  the  best 
three-tenths  obtainable,  non-adjustable;  but  there 


CHOICE   OF   OBJECTIVES   FOR    REGULAR    WORK.       211 

would  even  then  be  but  a  few  dollars  "  saved,"  with  the 
fact  staring  you  in  the  face  that  you  would  lose  all  your 
practice  with  an  adjustable  glass.  This  you  must  have, 
and  from  the  very  start. 

The  author  thus  dwells  on  this  matter  because  he  feels 
that  it  is  one  of  deep  interest  to  many.  It  is  one,  also, 
that  he  has  given  particular  attention  to,  that  he  might 
be  able  to  advise  others  intelligently;  and  he  is  not 
without  reason  to  hope  that  the  information  he  has  thus 
tried  to  convey  in  the  simplest  possible  language  will 
be  to  many  worth  more  than  the  cost  of  his  little  book. 
He  is  aware,  that  in  writing  the  last  page  or  two,  he 
has  been  practically  repeating  the  tenor  of  what  has 
before  been  written;  but  nevertheless  he  is  strong  in 
the  faith  that  more  than  one  of  his  readers  will  have  no 
fault  to  find  with  him  on  this  score.  To  those  about 
purchasing  an  outfit  of  objectives  he  would  further  say 
that  the  advice  here  given  is  precisely  what  he  has  given 
to  scores  of  enquirers  during  the  past  six  years,  every 
one  of  whom  have  expressed  their  satisfaction  in  a  man- 
ner not  to  be  mistaken.  Let  the  reader,  however,  be 
reminded  that  we  live  in  an  age  of  progress,  and  that 
it  is  quite  probable  that  the  instructions  offered  here  at 
this  date  may  at  no  distant  day  require  essential  modifi- 
cations. Doubtless  improvement  will  continue  to  follow 
improvement  in  the  future  as  well  as  in  the  past :  the 
genius  of  our  American  opticians  is  such  that  anything 
in  the  way  of  progress  successfully  accomplished  seems 
to  render  them  more  restless  than  before,  and  in  view 
of  this,  to  use  a  nautical  phrase,  we  advise  the  reader 


212  HOW   TO    SEE    WITH   THE    MICROSCOPE. 

to  keep  well  "  an  eye  to  windward."  And  it  may  be 
here  we  can  render  quasi  assistance,  thus : 

Judging  the  future  from  the  past,  it  seems  more  than 
likely  that  our  opticians  will  at  no  distant  day  produce 
one-fourth,  one-fifth  or  one-sixth  quite  equal  in  every 
respect  to  the  one-tenth  of  to-day,  and  possibly  with  a 
greater  working  distance.  The  author,  within  the  last 
twenty-four  hours,  has  received  reliable  testimony  af- 
firming that  young  Spencer  has  succeeded  in  making  a 
wet  and  dry  one-sixth  fully  up  to  the  performance  of 
the  one-tenth,  of  which  mention  has  before  been  made 
in  these  pages.  This  one-sixth  we  have  not  seen,  but 
are  informed  that  it  is  now  in  the  hands  of  an  eminent 
microscopist,  who  will  exhibit  it  at  the  Paris  expos- 
ition. 

Again  it  may  be  possible  that  the  optician  will  suc- 
ceed in  enlarging  the  aperture  of  the  low  powers. 
Heretofore  45°  has  been  regarded  as  the  limit  of  angle 
for  the  inch;  with  our  present  knowledge  it  appears 
almost  an  impossibility  to  extend  the  present  limit  much 
beyond  the  figure  named,  unless,  indeed,  the  calibre  of 
the  objective  be  increased.  It  will  be  advisable,  never- 
theless, to  bear  in  mind  that  in  the  late  march  of  ad- 
vancement of  the  American  objective,  several  desirable 
points,  formerly  declared  "  impossible"  have  been  mas- 
tered by  the  optician,  and  are  to-day  "  un  fait  accompli" 
Now  if  it  shall  be  so  that  the  optician  succeed  in  pro- 
ducing a  one-fourth  equaling  in  angle  and  performance 
the  present  work  of  the  one-tenth,  or  that  the  one-inch 
shall  in  the  future  rival  the  work  of  the  two-thirds  of 


SELECTION   OF   COVERING    GLASS.  213 

to-day,  then  will  the  superiority  of  such  glasses  be 
demonstrated,  and  for  reasons  already  given,  and  we 
are  disposed  to  look  in  this  direction  for  future  improve- 
ments. Let  the  reader  also  remember  that  the  item 
of  "  working  distance"  must  not  be  lost  sight  of.  For 
instance,  if,  in  the  extension  of  the  one-fourth  to  the 
capacity  of  the  present  one-tenth,  the  working  distance 
of  the  former  should  be  decreased  to  that  of  the  latter ; 
then  the  real  gain  would  be  comparatively  slight, 
amounting  practically  to  a  saving  of  a  few  dollars  in 
the  cost  of  the  glass.  The  true  problem  is  to  gain 
working  force  and  efficiency  without  sacrifice  of  work- 
ing distance.  We  recognize  what  has  been  accom- 
plished, and  the  recognition  is  suggestive  of  further 
advances  in  the  same  direction. 

SELECTION   OF   COVERING   GLASS. 

This  can  be  readily  obtained  of  the. dealers  either  in 
sheets  or  ready  cut  into  squares  or  circles,  and  of  any 
desirable  thickness.  As  to  the  mere  form  of  the  cover 
used,  that  is  a  matter  of  fancy;  but  the  thickness  ought 
to  correspond  to  the  working  of  the  objective.  We 
try  to  confine  ourselves  to  three  thicknesses  of  cover- 
ing glass,  namely,  one-seventieth,  one-one-hundred-and- 
twentieth  and  one-two-hundredth  of  an  inch.  These 
may  respectively  be  denominated  as  thick,  medium  and 
thin.  It  is  a  matter  of  the  first  importance  that  those 
working  first-class  objectives  should  be  well  posted 
as  to  the  thickness  of  cover  employed,  and  yet  this  tell- 
ing point  has  been  utterly  lost  sight  of  in  the  books. 


214  HOW   TO   SEE   WITH   THE   MICROSCOPE. 

For  example :  By  knowing  the  thickness  of  the  cover, 
one  is  enabled  to  approximately  adjust  the  objective  at 
sight,  and  thus  save  time.  We  have  thousands  of 
mounted  objects  in  our  cabinets,  and  every  cover  has 
been  measured  with  all  the  accuracy  obtainable.  Those 
who  have  long  had  their  attention  called  to  this  item 
can,  by  dint  of  practice  thus  obtained,  tell  closely  the 
thickness  of  the  cover  by  simply  feeling  it,  and  this,  let 
me  assure  the  novice,  is  an  accomplishment  worth  hav- 
ing. Said  the  veteran  microscopist  of  New  York,  Rev. 
Dr.  Armstrong,  to  the  author,  not  long  since,  "  It's 
astonishing  how  fast  you  work.  You  seem  to  be  in 
perfect  harmony  with  the  objective."  Now  the  secret 
of  the  fast  work  noticed  by  the  doctor  lay  in  the  fact 
that  I  knew  the  thickness  of  all  my  covers,  and  was 
thus  enabled  to  place  the  collar  of  the  object-glass  very 
closely  in  position  at  the  very  start;  and  not  only  this; 
I  was,  for  the  same  reason,  posted  as  to  the  use  of  water 
or  glycerine.  Now,  to  take  a  case  from  practice:  Sup- 
pose I  desired  to  examine  a  brand  new  mount.  Let  it 
be  a  difficult  diatom  this  time.  First,  I  run  my  finger 
over  the  cover  and  instantly  discover  that  it  is  a  thin 
one,  say  about  like  those  used  on  the  Moller  plates. 
Now,  if  I  elect  to  use  the  one-sixth  objective,  I  know  that 
this  cover  is  too  thin  for  water  immersion ;  hence  glycer- 
ine is  chosen.  I  know,  too,  that  over  such  a  cover,  and 
with  the  glycerine  intermedium,  the  objective  will  "  cor- 
rect "  some  three  or  four  divisions  from  closed ;  there- 
fore the  collar  is  at  once  placed  near  such  position. 
Now,  on  looking  through  the  tube  at  the  object  in  posi- 


SELECTION    OF    COVERING    GLASS.  215 

tion  and  focussecl,  suppose  I  do  not  get  as  good  views 
as  I  had  reason  to  expect,  then  I'let  the  collar  stand  as 
it  was  and  change  the  illumination  until  things  are  ap- 
proximately as  desired;  this  done,  a  slight  turn  of  the 
collar  adjustment  will  insure  the  maximum  working  of 
the  objective.  Now  just  contrast  this  with  the  usual 
"  modus."  Eiofht  operators  out  of  ten  would  have  at 
once  twisted 'round  the  collar  hap  hazard  like,  by  "  rule 
of  thumb,"  probably  wasting  plenty  of  time,  and,  more 
unfortunately  still,  condemning  a  really  good  objective, 
and  one  that  would  have,  with  the  proper  manipulations, 
given  charming  displays. 

Now,  in  the  instance  quoted,  we  took  the  mount  as 
we  found  it,  nnd  "handled"  it  as  best  we  could  with 
the  least  loss  of  time,  the  only  means  at  our  command 
being  the  choice  between  glycerine  and  water  as  the 
immersion  medium.  Now  suppose  the  mount  was  one 
prepared  with  especial  reference  to  a  one-twenty-fifth 
or  a  one-fiftieth,  and  having  an  extremely  thin  cover, 
say  one-four-hundredth  of  an  inch  thick.  Under  these 
circumstances  it  would  have  been  imperative,  to  suit 
the  work  of  the  one-sixth,  that  this  thin  cover  be  sup- 
plemented with  another  and  a  thicker  one,  making  opti- 
cal contact  with  water  or  soft  balsam.  This  ?,',<?  an  in- 
convenience which,  in  the  case  alluded  to,  cannot  be 
well  avoided ;  but  we  are  nevertheless  taught  the  pro- 
priety of  suitably  covering  such  mounts  as  may  be  pre- 
pared in  our  usual  line  of  practice.  All  this  seems  plain 
enough,  without  further  demonstration.  Let  the  tyro 
then  cover  his  mounts  as  far  as  possible^  to  suit  the 


216  HOW  TO   SEE   WITH   THE   MICROSCOPE. 

objectives  under  which  he  expects  to  show  them,  and 
let  him,  too,  early  learn  to  discriminate  as  to  the  dif- 
ferences in  thickness  of  covering  glass. 

A  handy  instrument  for  measuring  the  thickness  of 
thin  glass  is  a  little  pocket  micrometer  gauge  manufac- 
tured by  the  Brown  &  Sharp  Company,  of  Providence, 
R.  I.  Although  not  expressly  made  for  the  purpose,  it  is 
as  convenient  and  accurate  as  any  other  we  have  met, 
while  its  cost  is  very  moderate.*  We  make  it  a  plan  that 
when  a  quantity  of  new  covers  are  first  in  hand  to  pass 
them  over  to  the  pupil,  to  be  by  him  measured  with  the 
instrument  aforesaid,  and  assorted  according  to  their 
thickness,  the  various  styles  being  kept  in  little  boxes 
by  themselves,  and  duly  labeled.  In  this  way  the  stu- 
dent acquires  the  needful  practice,  and  the  requirements 
of  the  laboratory  are  met  at  the  same  time.  If  so  be 
that  no  instrument  of  the  kind  is  at  hand,  or  that  the 
observer  feels  that  he  cannot  afford  the  necessary  out- 
lay, the  usual  fine  adjustment  of  the  stand  can  be  made 
to  do  tolerably  effectual  duty,  thus :  Obtain  a  cover,  of 
which  the  thickness  is  known,  and  with  a  fine  pen  dipped 
in  thick  India  ink,  make  a  mark  on  one  surface  near  the 
centre;  turn  the  cover  over  and  make  another  similar 
mark  nearly,  but  not  exactly  opposite  the  first .  Now 
place  the  same  under  the  microscope,  focus  on  the  mark 
on  the  under  side  -of  the  cover,  and  then,  by  the  fine 
wheel  of  the  fine  adjustment,  focus  again  on  the  mark 
on  the  upper  surface,  noting  the  revolutions  or  parts 

*  As  we  have  before  remarked,  the  fine  adjustment  of  the  Acme  can  be 
used  as  a  micrometer. 


BECK'S   VERTICAL    ILLUMINATOR. 


217 


thereof  traversed  by  the  wheel.  By  this  simple  proced- 
ure a  gauge  is  established  from  which  other  covers  can 
be  easily  measured.  Some  stands  have  the  wheel  of  the 
fine  adjustment  graduated,  which  will  be  found  especially 
convenient.  In  other  cases  the  observer  can  make  his 
own  graduations  on  a  little  circle  of  paper  and  adapt 
the  same  to  the  wheel,  without  any  great  drain  on  his 
mechanical  skill. 


BECK'S   VERTICAL   ILLUMINATOR. 

This  instrument  consists  of  a  brass  tube,  either  end 
being  fitted  with  the  "  society  screw,"  so  that  it  can  be 
attached  to  the  back  of  the  objective;  the  object-glass 
with  the  iluminator  thus  attached  is  screwed  to  the  nose 
piece  of  the  stand.  The  tube  has  an  adapter  of  its  own, 
so  that  it  can  be  revolved  around  the  optical  axis  of  the 


218  HOW   TO    SEE    WITH    THE   MICROSCOPE. 

microscope.  In  this  tube  is  placed  a  circular  glass  disk 
(one  of  the  ordinary  circular  covers  used  in  mounting* 
object  slides).  This  disk  is  supported  in  position  by  a 
horizontal  pin,  to  which  it  is  fastened  with  a  bit  of  ce- 
ment, the  pin  passing  to  the  outside,  and  terminating 
with  a  little  knob,  by  which  the  disk  can  be  revolved 
at  will.  The  tube  is  pierced  laterally  with  an  aperture 
for  the  admission  of  light.  The  light  from  an  ordinary 
hand  lamp  passing  through  the  aperture  is  received  by 
the  little  glass  disk,  and,  by  turning  the  outside  knob 
properly,  is  made  to  pass  vertically  downwards  to  the 
rear  of  the  objective,  and  by  it  in  turn  concentrated  oil 
the  object  to  be  examined ;  no  sub-stage  or  other  illu- 
mination being  used.  This  is  the  instrument  as  made  by 
the  Messrs.  Beck,  and  is  in  fact  but  a  modification  of  a. 
similar  instrument  invented  by  Prof.  H.  L.  Smith,  of 
Geneva,  N.  Y.  Prof.  Smith's  device,  however,  is  fur- 
nished with  an  interior  metal  reflector  in  place  of  the 
glass  disk  of  the  instruments  of  the  Messrs.  Beck. 

We  had  used  the  illuminator  but  a  very  short  time 
when  we  discovered  that  the  definition  of  the  objective 
was  very  much  improved  by  shutting  off  the  area  of  the 
lateral  aperture,  thus  allowing  less  light  to  enter.  We 
also  found  that  the  actual  amount  of  light  needed  de- 
pended on  the  objective  employed.  In  most  instances 
the  higher  the  angle  of  the  object-glass,  the  smaller 
should  be  the  area  of  the  lateral  aperture. 

About  the  time  we  had  arrived  at  the  above  fact,  the 
Hon.  P.  H.  Watson  happened  to  call  in  to  spend  an 
hour  or  two  "  over  the  tube."  The  conversation  turn- 


BECK'S    VERTICAL   ILLUMINATOR. 

ing  on  the  action  of  the  Beck  illuminator,  we  coupled  the- 
instrument  to  my  Tolles  one-tenth  and  worked  them 
over  Mr.  Watson's  Nobert  test-plate,  and  in  a  very  short 
time  succeeded  in  getting  a  most  charming  display  of 
the  19th  band,  and  while  the  latter  aperture  was  nearly 
closed  by  interposing  the  circular  edge  of  a  large  bull's 
eye  condenser  which  happened  to  be  at  hand  on  the 
table.  Mr.  Watson  and  myself  were  both  delighted 
with  the  exquisitely  beautiful  display  of  this  so-called 
difficult  object — this  19th  band.  Other  severe  tests 
were  also  taken  in  hand  and  resolved.  Among  others 
we  had  a  glorious  show  of  podura  under  amplifica- 
tion of  some  4,000  diameters.  It  was  demonstrated, 
too,  that  the  very  best  resolutions  were  only  obtained 
when  more  or  less  of  the  lateral  aperture  was  closed  by- 
interposing  the  circular  rim  ot  the  condenser,  the  clear 
aperture  left  being  in  the  form  of  a  crescent.  Subse- 
quently Mr.  Watson  devised  the  following  described, 
attachment,  which  answers  the  purpose  fully : 

The  lateral  aperture  of  the  instrument  is  somewhat 
enlarged  and  a  hollow  plug  inserted  therein,  the  opening 
in  this  plug  being  the  same  calibre  as  the  original  aper- 
ture. The  plug  is  somewhat  tapering,  and  fits  the  open- 
ing "  spring  tight."  It  also  projects  outward  slightly 
beyond  the  circumference  of  the  main  tube.  To  the  outer 
end  of  the  plug  is  fitted  a  little  shutter,  while  a  narrow 
slit,  about  one-one-hundred-and-fiftieth  of  an  inch  wider 
is  pierced  through  the  shutter;  the  whole  so  arranged 
that  the  opening  the  plug  can  be  partly  or  wholly  closed 
or  the  little  slit  used  by  itself;  and  when  low  powers  are 


220  HOW   TO   SEE   WITH   THE   MICROSCOPE. 

employed,  or  objectives  of  narrow  apertures  used,  the 
entire  attachment  can  be  removed  if  desired.  This 
illuminator,  as  originally  designed,  was  intended  for 
use  with  dry  objectives  and  with  moderate  magnifica- 
tions; the  idea  of  using  it  with  immersion  glasses  of 
high  angles  and  under  high  powers,  originated  with 
George  W.  Morehouse,  Esq.,  of  Wayland,  New  York, 
who  is  well  known  as  an  expert  and  accomplished  mi- 
-croscopist.  The  special  advantages  obtained  by  the 
immersion  system  in  the  case  in  hand  are  too  apparent 
to  need  further  mention.  It  will  be  noticed,  too,  that 
the  Beck  is  thus  made  to  do  duty — like  the  Wenham 
reflex — in  a  way  quite  foreign  to  the  purpose  of  its 
original  inventor. 

The  advantages  derived  by  the  use  of  the  instrument 
are :  First,  we  are  thus  enabled  to  view  objects  by  the 
aid  of  reflected  light;  the  so-called  "opaque  illumina- 
tion," under  the  highest  amplifications  and  (if  the  proper 
objective  be  employed)  with  superb  definition,  as  is 
attested  by  its  unequaled  work  over  the  Nobert  19th 
band ;  and  by  the  employment  of  artificial  light,  a  com- 
mon kerosene  hand-lamp  being  all  that  is  required.  In 
this  respect  the  instrument  stands  alone  and  inimitable. 
Second,  the  views  given  are  surface  markings  only. 
There  is  no  "penetration"  here.  The  focus  must  be 
most  accurately  drawn,  and  on  the  surface  of  the  object. 
The  slightest  deviation  therefrom  is  instant  and  total 
defeat.  Thus  we  are  enabled  to  locate  structure,  at 
times  a  most  valuable  assistance  to  the  observer.  Third, 
by  a  slight  change  in  the  position  of  the  lamp,  the  mir- 


BECK'S   VERTICAL   ILLUMINATOR.  221 

ror  being  at  the  same  time  brought  into  play,  the  illu- 
mination may  be  almost  instantly  changed  to  that 
of  transmitted  light,  or  from  thence  back  to  reflected 
light  again.  This  cross-questioning  under  two  methods 
of  illumination  is  often  of  great  advantage. 

Per  contra :  The  vertical  illuminator  has  but  one 
drawback,  and  that  is  rather  a  serious  one,  to  wit:  Ob- 
jects to  be  displayed  under  it  must  be  mounted  dry,  and 
also  contact  the  cover.  Hence  it  will  be  seen  that  a 
large  portion  of  histological,  pathological,  as  well  as 
other  permanent  mountings,  are  excluded  from  use. 
Many  of  these  can  be  temporarily  prepared  for  study, 
and  it  is  hoped  that  the  attention  of  observers  will  be 
enlisted  in  this  direction.  Admitting  the  serious  char- 
acter ot  the  objection  named,  let  us  bear  in  mind  that 
there  remain  countless  fields  of  research  wherein  the 
"Beck"  will  certainly  prove  an  instrument  of  the 
greatest  value. 

The  tyro  will  find  the  Beck  illuminator  a  difficult  in- 
strument to  use,  and  his  first  attempts  will  probably 
result  in  failure.  Nor  is  it  an  easy  task  to  give  any 
instruction  in  writing  that  will  be  of  much  aid.  The 
instrument  not  being  a  costly  one,  and  likely  to  be  gen- 
erally used  when  it  shall  become  better  known,  we  will 
try  and  furnish  a  few  hints  that  perchance  may  prove 
of  value  to  the  beginner. 

The  novice  will  do  well,  at  his  first  attempts,  to  select 
a  dry  mount,  one  that  he  is  perfectly  familiar  with,  and 
preferably  scales  from  the  lepidoptera;  a  dry  mount  of 
podura  will  answer  very  well,  indeed.  Select,  also,  the 


222  HOW  TO    SEE   WITH  THE   MICROSCOPE. 

highest  angled  objective,  and  with  this  examine  the 
mount  in  the  ordinary  way  and  get  a  tolerable  correc- 
tion for  the  glass.  Next,  removing  the  object-glass 
from  the  stand,  couple  it  to  the  illuminator  and  screw 
the  whole  to  the  nose-piece  of  the  stand,  using  trans- 
mitted light,  as  usual.  Focus  the  objective.  Now  hunt 
through  the  slide;  among  the  numerous  scales  will 
probably  be  found  one  or  two  which,  in  order  t<"»  bring 
in  focus,  the  objective  will  require  to  be  withdrawn  from 
the  cover  slightly.  In  such  a  case  the  chances  are  that 
that  particular  scale  is  nearer  the  cover,  and  if  in  good 
condition  may  be  selected  for  further  operations.  Next, 
bring  the  lamp  (a  flat  wicked  one)  towards  the  observer, 
revolving  the  tube  of  the  illuminator  so  that  the  lateral 
.aperture  shall  be  in  proper  position  to  receive  the  light 
from  the  lamp,  the  latter  being  about  seven  or  eight 
inches  distant,  and  the  flame  about  the  same  height  as 
the  aperture  of  the  illuminator.  Now  grasp  the  little 
knob  connected  with  the  interior  glass  disk  and  turn  it 
^so  that  light  shall  be  reflected  to  the  rear  of  the  object- 
ive ;  at  the  same  time,  and  looking  through  the  tube  as 
you  catch  the  first  glimpse  of  light,  revolve  simultane- 
ously the  main  tube  and  also  the  little  knob  carrying 
the  glass  disk,  the  object  being  to  secure  as  great  an 
amount  of  light  as  possible.  A  little  manipulation  of 
this  kind  ought  to  result  in  illuminating  the  object  with 
a.  horizontal  (or  nearly  so)  band  of  light.  The  next 
step  will  be  by  a  slight  movement  of  the  lamp,  keeping 
its  edge  exactly  towards  the  aperture,  to  endeavor  to 
make  the  band  of  light  crossing  the  field  as  narrow  as 


WORKING   WITH   LOW  POWERS.  223 

possible,  and  the  outlines  of  the  band  clear  and  distinct. 
By  this  time  the  operator  will  have  probably  discovered 
that  a  slight  rotation  of  the  main  tube  will  separate 
the  horizontal  band  into  two  parts,  or,  as  some  of  my 
pupils  express  it,  "  two  tongues."  The  best  position  is 
when  these  are  made  to  coalesce  as  completely  as  possible. 
It  is  also  probable  that  in  the  attempts  thus  far  made 
that  the  imaofe  of  the  scale  has  been  well  seen.  When 
this  occurs  it  should  be  at  once  focussed.  The  next 
procedure  is  to  correct  the  objective;  the  correction 
obtained  by  transmitted  light  will  not  suffice  for  the 
purpose  in  hand.  It  will  be  noticed  that  as  the  glass  is 
made  to  approach  the  correct  adjustment,  the  horizontal 
band  of  light  will  be  correspondingly  improved.  So 
true  is  this,  that  one  might  almost  be  governed  thereby 
in  the  adjustment  of  the  objective.  Having  got  thus 
tar  along,  and  without  any  serious  mishap,  it  will  be 
•easy,  by  closing  the  shutter,  to  admit  the  precise  and 
most  favorable  amount  of  light,  and  also  to  try  the 
effect  of  sundry  very  slight  changes  in  the  position  of 
the  main  tube,  glass  disk  and  lamp.  Very  beautiful 
resolutions  are  sometimes  obtained  by  bringing  the  lamp 
within  five  or  six  inches  and  interposing  the  bull's  eye 
condenser,  flat  side  to  the  lamp,  in  which  case  the  shut- 
ter must  be  further  closed.  It  will  happen  also,  occa- 
sionally, that  the  best  exhibition  of  striae  on  very  diffi- 
cult objects,  such  as  extremely  close  fmstulia  saxonieas, 
is  when  the  striae  are  placed  at  right  angles  to  the  hori- 
zontal band  of  light. 

Now,  should  the  manipulator  meet  with  tolerable  sue- 


224  HOW   TO    SEE   WITH   THE   MICROSCOPE. 

cess,  and  get  good  shows  of  the  lepidoptera,  I  recom- 
mend that  he  practice  for  some  half-dozen  sittings  over 
the  same  mount.  By  this  he  will  get  a  certain  familiarity 
with  the  instrument  which  will  be  of  great  value  to  him. 
The  chances  are,  too,  that  he  will  wonderfully  improve 
in  the  manipulations,  and  in  this  alone  will  be  well 
enough  rewarded  for  his  pains.  Furthermore,  he  will 
learn  what  nice  effects  can  be  had  by  the  slightest  changes 
in  the  position  of  the  tube,  glass  disk,  shutter  or  lamp, 
and  the  necessity  for  the  closest  focussing  will  be  taught 
practically. 

Having  thus  got  tolerably  acquainted  with  the  instru- 
ment, let  the  operator  try  changing  from  reflected  to- 
transmitted  light,  and  vice  versa,  which  is  accomplished 
merely  by  moving  the  lamp  back  to  its  first  position,, 
employing  the  mirror  just  as  was  recommended  at  the 
start.  A  little  practice  of  this  nature,  working  alter- 
nately by  transmitted  and  reflected  light,  will  soon 
accustom  the  observer  to  the  situation,  and  enable  him 
to  make  the  change  in  illumination  almost  instantly. 

A  fact  worth  knowing  is  this :  The  combined  length  of 
the  illuminator  and  objective  will,  if  the  objective  selected 
be  one  of  the  extremely  long  models,  defeat  its  use  on 
some  of  the  smaller  stands.  Thus  we  find  that  we  can- 
not use  the  illuminator  with  a  Tolles  one-sixth  or  one- 
tenth  on  the  little  "  Histological"  of  Mr*.  Zentmayer, 
there  not  being  sufficient  room  between  the  "jacket'* 
in  which  the  body  tube  slides  and  the  stage  to  receive  the 
illuminator  and  objective  when  coupled  together.  We 


BULL'S    EYE    CONDENSER. LO\V    POWERS.  225 

are  therefore,  when  essaying  the  use  of  the  Beck,  com- 
pelled to  fall  back  on  a  larger  and  heavier  stand.* 

BULL'S    EYE    CONDENSER. 

This  instrument,  so  well  known,  and  accompanying 
almost  every  stand  as  sold,  we  make  nearly  constant  use 
of.  It  should  be  simply  a  large  plano-convex  lens,  say 
from  two  to  three  inches  in  diameter,  and  fitted  with 
universal  mountings.  It  has  been  too  general  a  rule  with 
the  microscope  makers  to  "adapt"  the  size  of  the  con- 
denser to  that  of  the  stand.  Thus,  if  a  certain  maker 
furnish  five  or  six  different  sizes  of  stands,  he  will  be 
pretty  sure  to  have  as  many  sizes  of  condensers  to  accom- 
pany the  same.  But  let  the  reader  insist  that,  however 
small  may  be  the  model  of  the  stand  selected,  the  con- 
denser be  at  least  two  inches  in  diameter,  and  that  even 
three  inches  will  be  found  none  too  large.  Any  of  our 
opticians  can  furnish  the  instrument  made  to  order. 
We  have  seen  and  worked  with  several  made  by  Zent- 
mayer  to  accompany  his  large  and  intermediate  stands, 
and  also  the  large  model  furnished  with  the  Messrs. 
Beck,  all  of  which  were  effective  instruments. 

WORKING   WITH  LOW   POWERS. 

It  has  been  our  primary  intention  throughout  this 
work  to  avoid  repetition  of  instructions,  hints  or  sug- 
gestions, such  as  may  be  found  in  the  various  text- 
books, while  interspersed  among  the  pages  already  writ- 

*  The  construction  of  the  "Acme"  admits  the  use  of  the  Beck  illumina- 
tor. 

15  Microscopy. 


226  HOW   TO   SEE   WITH   THE   MICROSCOPE. 

ten  the  reader  may  perhaps  recognize  information  as  to 
every  day  work  which,  perchance,  he  may  turn  to  some 
account.  There  remains  therefore  but  little  for  us  to 
ndd  under  the  above  caption.  Without  hesitating  to 
repeat  in  a  more  condensed  form  the  same  ideas  which 
liave  heretofore  been  scattered  through  our  pages,  we 
proceed  to  give  other  methods  of  working  with  the 
lower  powers. 

First,  we  use  and  recommend  a  stand  fitted  with  a 
swinging  sub-stage,  preference  being  given  to  the  one 
that  will  allow  the  mirror  to  rise  above  the  level  of  the 
stage.  Stands  there  are  which  although  allowing  a  lim- 
ited swing,  do  not  afford  the  extreme  range  of  motion, 
while  scores  there  be  fitted  with  stationary  sub-stages 
and  fittings.  Of  the  last  two  named,  that  with  the  lim- 
ited range  is  infinitely  to  be  preferred.  One  of  the  prin- 
cipal advantages  arising  from  swinging  the  mirror  above 
the  stage  is  that  we  are  enabled  thus  to  condense  either 
sun  or  artificial  light  on  the  top  of  the  object,  and  it  is 
possible  to  accomplish  this  otherwise  than  by  the  swing, 
by  simply  attaching  a  mirror  to  a  separate  adjustable 
stand  of  its  own.  In  whatever  arrangement  which  may 
be  selected,  let  it  be  imperative  that  the  mirror  be  attached 
directly  to  the  swinging  arm,  and  at  the  proper  focal 
distance,  and  that  the  centre  of  rotation  coincide  with 
the  plane  of  the  object  on  the  stage.  Any  adjustable 
and  intermediate  joints  between  the  mirror  and  the 
swinging  arm,  allowing  the  former  to  be  placed  out  of 
ite  focal  position,  is,  in  the  opinion  of  the  author,  an 
intolerable  nuisance,  and  one  not  to  be  submitted  to  un- 


WORKING   WITH   LOW   POWERS.  227 

der  any  conditions  short  of  sheer  necessity.  Now  of  ths 
two  styles  of  stands,  the  one  with  the  full  swing  and 
the  other  with  the  partial  swing  only,  premising  that 
both  mirrors  rotate  in  the  plane  of  the  object,  there 
will  not  be  a  great  deal  of  choice  for  general  work. 
Nevertheless  it  costs  no  more  to  manufacture  the  one 
than  the  other,  and  hence  the  perfect  stand  becomes  no 
more  costly  than  one  that  is  to  a  certain  extent  imper- 
fect. Therefore  we  urge,  why  not  procure  the  best, 
provided  there  are  not  especial  and  governing  conditions 
patent  to  the  purchaser.  The  substance  of  all  this  has 
been  placed  before  the  reader,  and  in  again  calling  his 
attention,  it  is  hoped  that  the  repetition  will  gather 
force. 

Now  all  the  information  we  have  to  offer  as  to  working 
with  the  low  powers  will  refer  entirely  to  the  use  of  the 
low-angled  sub-stage  condenser  conjointly  with  such  a 
stand  as  we  have  recommended.  As  has  been  before 
remarked,  the  introduction  of  the  swing  has  worked  a 
radical  change  in  our  ideas  as  to  the  value  of  the  con- 
denser, and  the  instrument  is  now  with  us  a  constant 
fixture,  and  in  daily  use. 

With  the  use  of  the  condenser  we  have  at  command  a 
greater  amount  of  light,  but  this  is  not  the  special  advan- 
tage derived  from  its  use ;  and  then  again  it  is  easy  to  make 
the  bull's  eye  do  duty  in  its  place.  Of  the  two  accessories, 
the  bull's  eye  is  the  more  simple  and  convenient  to  use; 
nor  will  objects  occupying  the  entire  or  greater  portion 
of  the  field  when  illuminated  with  the  condenser  appear 
more  brilliant  and  enticing  than  without  it.  The  grand 


228  HOW  TO    SEE    WITH   THE   MICROSCOPE. 

advantage  obtainable  with  the  condenser  is,  that  by  a 
careful  manipulation  of  the  apex  of  the  small  cone  of 
light  we  are  often  able  to  get  just  the  right  illumination 
on  certain  details  of  our  object,  while  the  field  generally 
is  kept  in  partial  light  only,  "  toned  down"  as  it  were. 
This  effect  may  be  produced  in  two  ways:  First,  by 
raising  or  lowering  the  condenser;  and,  secondly,  by 
swinging  the  sub-stage  laterally  to  a  point  but  just 
within  the  aperture  of  the  objective  employed.  We 
sometimes  use  the  one  plan  and  sometimes  the  other; 
and  then,  again,  we  often  use  a  mixture  of  both,  and, 
as  a  rule,  the  better  illumination  will  be  attained  when 
the  condenser  is  somewhat  within,  or  without  the  focal 
point. 

Now  let  the  novice  understand  that  in  thus  employ- 
ing the  condenser  there  is  no  attempt  to  get  "  pretty  dis- 
plays "  of  the  object.  On  the  other  hand,  the  primary 
object  is  to  obtain  cool  and  reliable  definition  of  struct- 
ture.  Those  who  thus  use  it  will,  I  think,  be  pleased 
with  the  results  attained.  It  is  somewhat  more  "  bother  " 
than  taking  ^he  light  directly  from  the  mirror,  or  with 
the  usual  intervention  of  the  diaphragm.  Notwith- 
standing this,  one  soon  becomes  accustomed  and  addicted 
to  its  use.  The  swinging  stage,  too,  is  a  valuable  ad- 
junct to  the  old  diaphragm,  and  with  this  latter  instru- 
ment superior  effects  can  be  had  working  on  the  same 
general  plan  as  with  the  condenser,  and  using  a  small 
aperture  to  the  diaphragm.  Should  the  light  be  too 
weak  it  can  be  assisted  by  interposing  the  bull's  eye,  or 
light  can  be  shut  off  by  depressing  the  diaphragm. 


WORKING    WITH   LOW   POWERS.  2'2 V 

For  ordinary  work  by  daylight  we  use  the  plain  mir- 
ror in  conjunction  with  the  condenser;  and  let  roe  here 
again  insist  that  the  latter  be  such  as  has  already  been 
described,  i.  e.,  of  low  aperture,  admitting  but  a  narrow 
cone  of  light.  In  very  dark  days  the  light  can  be  rein- 
forced by  employing  the  concave  mirror,  a  plan  not  gen- 
erally recommended,  but  nevertheless  quite  practicable. 

For  reasons  before  given*  we  greatly  prefer,  for  regu- 
lar right  straight  along  daily  work,  to  use  the  stand 
with  the  tube  short,  keeping,  for  the  most  part,  the 
tube  vertical,  dispensing,  too,  with  the  stage  clips,  and 
simply  laying  the  preliminary  mount  thereon,  shoving 
it  about  in  every  direction  required,  by  the  fingers. 
Those  who  have  been  accustomed  to  confine  the  slide 
under  the  clips,  as  is  generally  done,  will  not,  on  the 
first  trial,  be  likely  to  endorse  my  practice.  Let  me, 
then,  to  all  such,  especially  recommend  it.  By  thus 
allowing  the  slide  to  rest  by  its  own  gravity  alone,  one 
soon  acquires  a  delicacy  of  finger  manipulation  that  is 
of  very  general  value;  while, per  contra,  the  clips  are  a 
real  hindrance  to  fast  work.  Those  who  have  the  pa- 
tience to  practice  without  them  for  one  solitary  week 
will  not  be  likely  to  get  buck  into  the  old  rut. 

The  height  of  the  work  table  should  vary  with  that 
of  the  observer ;  such  a  table  as  one  would  naturally 
elect  to  write  on  will  be  about  the  correct  height  for 
microscope  work.  This,  if  the  low  angled  condenser  is 
to  be  generally  employed,  may  be  placed  at  a  consid- 
erable distance  from  the  window,  but  care  should  be 
taken  that  the  light  comes  from  the  left.  If  there  be 


230  HOW  TO   SEE   WITH   THE   MICROSCOPE. 

other  glazed  openings  in  the  room  liable  to  form  cross- 
lights,  they  should  be  closed  by  shutter  or  curtain. 
The  table  selected  should  be  solid  and  heavy.  Any  and 
all  of  the  little  light  affairs  in  cherry  and  mahogany 
offered  at  the  furniture  stores  are  totally  unfit  for  a  mi- 
croscope table;  but  the  crowning  nuisance  of  the  lot  is 
the  revolving  table,  made  expressly  for  the  microscopist, 
and  sold  at  outrageous  prices.  Castors,  also,  are  to  be 
rejected.  In  short,  anything  that  detracts  from  the  sol- 
idity or  rigidity  of  the  work-table  is  to  be  eschewed. 
What  the  observer  wants  is  a  firm  support  for  his  stand, 
free  from  shake  or  tremble — one  that  he  can  lean  against 
freely  when  weary,  and  one  that  he  may  even  run  against 
accidentally  without  inaugurating  any  serious  calamity. 
A  couple  of  drawers  placed  in  the  front  are  a  convienience 
for  storage  of  accessories,  etc.,  and  these,  being  partly 
opened,  form  convenient  rest  at  times  for  the  forearm. 
The  table  should  be  sufficiently  large  and  roomy.  Three 
by  four  feet  is  none  too  large. 

THE    SPENCER    ONE-INCH    OF   50° — BROAD-GUAGE   OBJECT- 
IVES, ETC. 

In  the  spring  of  1878  we  received  from  the  Messrs. 
Spencers  an  inch  objective  of  50°  aperture.  This  glass 
was  made  expressly  to  our  own  order. 

Our  purpose  in  ordering  the  above  glass  was  to  deter- 
mine whether  it  was  possible  for  the  Messrs.  Spencers 
to  furnish  an  inch  objective  having  angle  and  definition 
equal  to  their  celebrated  two-thirds. 

With  the  new  inch  our  experience  has  thus  far  been 


BROAD-GUAGE  OBJECTIVES,  ETC.  231 

necessarily  limited;  we  have,  however,  instituted  a  few 
comparative  tests  which  we  now  present  to  our  readers. 

The  working-  distance  of  the  two-thirds  worked  with 
one- fourth  inch  solid  ocular  and  standard  ten-inch  tubes 
is  twenty -five-one-hundredths  of  an  inch. 

The  working  distance  of  the  new  inch  with  same  oc- 
ular, worked  with  ten-inch  tube,  is  thirteen-one-hun- 
dredths  of  an  inch ;  when  worked  with  the  same  eye-piece 
and  the  short  tube  of  the  "  Histological,"  the  working- 
distance  is  increased  to  eighteen-one-hundredths  of  an 
inch. 

In  general,  the  definition  of  the  inch  is  superior  to 
that  of  the  two-thirds.  The  very  best  definition  of  the 
latter  is  obtained  by  the  use  of  the  full  length  tube  and 
one-fourth  inch  ocular,  while  the  highest  definition  of 
the  inch  is  reached  by  the  use  of  the  short  tube  and 
same  ocular. 

The  inch,  worked  over  the  balsamed  Moller  plate,  gives 
readily  nice  shows  of  the  transverse  striae  of  P.  Balti- 
cum,  and  with  a  little  management  both  sets  of  lines 
are  brought  out.  On  the  G.  Marina,  immediately  pre- 
ceding the  Balticum,  and  really  the  more  difficult  shell, 
the  inch  gave  me  a  very  nice  stand  of  the  transverse 
striae  from  end  to  end  of  the  shell,  its  performance  over 
this  diatom  being  manifestly  superior  to  that  of  the 
two-thirds. 

On  dry  mounted  shells  of  the  P.  Balticum  the  two 
sets  of  lines  are  very  well  displayed  by  the  inch,  as  are 
also  the  transverse  striae  of  dry  angulatum,  a  favorable 
frustule  being  selected. 


232  HOW   TO   SEE   WITH   THE   MICROSCOPE. 

Over  the  Nobert  test  plate  the  inch  gave  me  the  9th 
band,  =  56  X  lines  in  .001,  Eng.  inch. 

Working  the  two-thirds  with  the  one-half  inch  ocular 
and  full  length  tube,  and  the  inch  with  one-fourth  inch 
ocular  and  short  tube,  the  amplifications  were  about 
equal ;  the  inch  in  every  instance  affording  the  better 
definition. 

According,  then,  to  the  inch  manifest  superiority  in 
point  of  denning  power,  its  shorter  working  distance, 
which  in  its  most  favorable  aspect  is  33  per  cent,  less 
than  that  of  the  two- thirds,  must  receive  due  consider- 
ation, this  decrease,  too,  of  working  distance  will  be 
accompanied  by  some  loss  of  "penetrating  power." 

A  mueh  mort  important  point,  however,  to  the  author 
was  to  ascertain  if  the  focal  distance  of  the  inch  was 
sufficient  to  allow  its  being  worked  over  wet  and  uncov- 
ered mounts  without  clouding  from  the  evaporation. 
To  test  this,  we  used  the  glass  an  entire  evening  in  reg- 
ular routine  work  over  urinary  deposits,  and  without 
experiencing  the  least  trouble  from  the  source  named ; 
while  on  the  other  hand  the  general  behavoir  of  the 
objective  while  thus  engaged  in  practical  work  was  most 
satisfactory. 

The  reader  is  reminded  that  in  comparing  working 
distances  of  long  focus  glasses,  the  same  percentage  of 
weight  does  not  obtain  as  would  occur  in  comparisons 
of  object-glasses  of  nominally  short  focal  lengths,  and 
giving  high  amplifications. 

A  word  or  two   concerning  the  standard  "  society 


BROAD-GUAGE  OBJECTIVES,    ETC.  233 

After  experimenting1  with  the  wide-angled  inch,  as 
above  related,  we  wrote  to  the  Messrs.  Spencers,  asking 
them  if  it  wTas  possible  either  to  still  further  extend  the 
angle  of  the  inch,  or,  maintaining  the  same  aperture, 
to  increase  its  working  distance.  In  reply,  the  elder 
Spencer  informed  me  that  it  would  be  difficult  to  fur- 
ther increase  the  aperture  or  the  working  distance  unless 
the  diameter  ot  the  objective  should  also  be  enlarged. 

From  this  it  would  seem  desirable  to  increase  the  di- 
ameter of  our  low-power  object-glasses,  and  this  in  turn 
necessitates  a  change  in  the  construction  of  the  micro- 
scope stand.  Mr.  Bullock's  large  stand,  as  also  the  Acme, 
are  especially  arranged  to  accommodate  these  "  broad- 
gauge"  low-power  objectives. 

An  one  inch  objective  of  large  calibre  is  now  in  pro- 
cess of  construction  for  the  author.  The  optician  hopes 
to  endow  it  with  an  aperture  of  at  least  62°,  maintain- 
ing a  working  distance  of  one-eighth  of  an  inch. 

It  is  but  a  simple  act  of  justice  to  say  that  the  idea 
-conveyed  to  me  by  Mr.  Spencer  had  already  occurred  to 
Dr.  W.  W.  Butterfield,  of  Indianapolis,  Ind.  While 
in  attendance  at  the  congress  of  microscopists  held  in 
Indianapolis  in  1878,  Dr.  Butterfield  showed  me  a 
broad-gauge  four-inch  made  to  his  order  by  London 
opticians.  He  had  also  a  stand  then  in  process  of  con- 
struction, and  designed  for  the  use  of  this  class  of  ob- 
ject-glasses. This,  however,  at  the  date  mentioned,  had 
not  arrived;  consequently  there  were  no  accommoda- 
tions for  an  examination  of  the  objective.  Should  my 
own  glass  be  completed  before  these  sheets  go  to  press, 


234  HOW   TO    SEE   WITH   THE   MICROSCOPE. 

some  account  of  its  performance  may  herein  be  expected. 
Meanwhile,  there  seems  to  bo  no  good  reason  why,  with 
the  increase  of  calibre  of  our  low-power  objectives,  there 
should  not  also  obtain  those  advantages  due  to  aperture 
M.nd  working  distance. 


CHAPTEE  VH. 

WORK  WITH  THE  HIGHER  "  POWERS." 

For  this  class  of  work  we  have  in  the  preceding  pages- 
unhesitatingly  expressed  our  preference  in  favor  of  ob- 
jectives of  the  widest  aperture.  Such  are  the  instru- 
ments we  ourselves  use  daily,  and  can  confidently  recom- 
mend to  all  who  may  be  desirous  of  working  with  the 
best  instrumentation  obtainable.  Therefore,  whatever 
we  may  have  to  offer  in  the  way  of  instructions  sug- 
gested by  the  above  heading  will  be  solely  applicable- 
to  the  class  of  objectives  generally  known  as  "  wide- 
angled,"  to  which  we  have  given  in  the  past,  and  pro- 
pose yet  to  give  in  the  Future,  a  large  amount  of  careful 
study  and  attention.  And  first  of  all  it  becomes  neces- 
sary to  disabuse  the  mind  of  the  student  of  some  of  the 
popular  fallacies  which  have  found  outlet  and  circulation 
through  the  medium  of  the  microscopical  periodical 
literature  of  the  present  and  past  few  years.  These,  a& 
will  be  discovered  by  the  attentive  observer,  are  par- 
oxysmal in  their  nature ;  in  fact  are  veritable  "  chateaux 
en  espagne,"  at  once  inconsistent  in  detail,  and  roundly 
absurd  when  contemplated  as  an  entirety.  Thus  it  oc- 
curs that  at  one  moment  the  student  is  taught  that  wide- 
angled  glasses  are  extremely  inconvenient;  that  great 
attention  has  to  be  bestowed  on  the  adjustment  and  illu- 
mination, etc. ;  while  on  the  other  hand,  another  "  au- 

235 


236  HOW   TO    SEE    WITH   THE   MICROSCOPE. 

thority"  subsequently  insists  that  the  so-called  "hand- 
ling" (?)  supposed  to  be  necessary  to  the  use  of  the 
wide  apertures  is  simply  a  myth — a  downright  farce; 
and  that  any  one  possessing  a  fair  quota  of  intelligence 
•can  easily  acquire  all  that  is  to  be  acquired  in  the  work- 
ing of  an  adjustnl>le  glass.  Nor  need  one  hunt  long  or 
dig  very  deep  to  find  other  "  authorities"  teaching  that 
all  this  handling"  "  although  essential  to  the  optician" 
is  no  manner  of  use  to  the  practical  observer,  unless  he 
has  so  far  degenerated  as  to  aspire  to  the  distinction  of 
being  simply  a  "  handler  "  and  a  "  fighter." 

Let  the  author,  then,  and  in  view  of  the  situation  as 
presented,  inform  those  proposing  to  study  the  microscope 
with  the  intention  of  becoming  in  due  time  accomplished 
observers,  that  there  is  no  "  royal  road  "  to  success ;  that 
to  become  even  so  sufficiently  expert  as  to  enable  one 
to  follow  out  (leaving  original  work  out  of  considera- 
tion) the  investigations  already  made  and  published  by 
eminent  microscopists,  will  require  quite  as  much  effort 
and  study  as  would  be  called  for  in  graduating  from  any 
college  in  the  United  States.  The  curriculum  is  a  broad 
one  in  its  very  nature,  involving  a  thorough  knowledge 
of  instrumentation,  and  when  by  means  thereof  we  are 
enabled  to  see  well,  it  then  becomes  a  positive  necessity 
to  judge  well  of  what  is  seen,  and  this  in  turn  can  only 
be  well  accomplished  by  those  having  eyes  well  trained 
to  the  work  in  hand.  There  is,  moreover,  work  for  the 
brain  outside  of  the  functions  of  the  optic  nerve. 

In  the  micrographic  dictionary,  by  Messrs.  Griffith  & 
Henfrey,  I  find,  (page  11,)  the  following:  "  Above  all. 


WOKK   WITH   THE     HIGHER    "  POWERS."  237 

however,  it  must  never  be  forgotten  that  microscopic 
investigations  require  more  time  and  patience  than  per- 
haps any  others,  even  in  regard  to  the  determination  of 
simple  facts  of  structure  and  qualitative  composition ; 
and  although  it  is  not  very  uncommon  to  hear  those  en- 
gaged in  them  sneered  at  as  wasting  their  time  over  a 
very  simple  plaything,  this  may  be  regarded  as  arising 
from  one  of  those  prejudices  which  will  exist  so  long  as 
people  will  venture  to  express  opinions  upon  matters  with 
which  they  are  unacquainted,  and  which  are  beyond  their 
comprehension." 

The  above  quotation  is  well  worth  reprinting  on  its 
intrinsic  merits,  and  it  may  be  that  we  shall  find  some 
especial  use  for  it  bye-and-bye.  Meanwhile,  this  mat- 
ter of  eye  training  calls  for  a  word  or  two,  for,  among 
the  accomplishments  tha/t  go  to  make  the  first  class  ob- 
server, this  education  of  the  eye.  is  generally  supposed 
to  be  quite  as  much  a  myth  as  the  capacity  to  "  handle  " 
an  object  glass.  Let  us  take  an  item  or  two  from  our 
personal  experience : 

Not  long  since  the  author  had  the  honor  to  address  a 
select  party  of  gentlemen  at  the  parlors  of  a  private 
residence.  In  the  course  of  his  remarks  the  matter  of 
"  eye-training  "  was  brought  prominently  forward  and 
its  usefulness  urgently  insisted  on.  Subsequent  to  the 
close  thereof  a  gentlemen  present  stepped  up  to  him, 
saying,  "  I  want  a  little  talk  with  you  about  that  eye 
business,  which  you  seem  to  regard  as  a  sine  qua  non. 
I  do  not  see  that  thing  as  you  do.  You  and  I  are  about 
the  same  age.  We  have  both  of  us  necessarily  been 


238  HOW   TO   SEE   WITH   THE   MICKOSCOPE. 

using  our  eyes  constantly  all  our  days.  If  I  look  across 
the  street  and  see  a  house,  why,  so  can  you;  and  thus 
we  have  been  respectively  seeing  houses  as  well  as  other 
things  all  through  life.  In  short,  our  eyes  have  been 
constantly  at  work,  and  have  thus  been  as  constantly 
trained.  It  may  be  that  you  have  abused  yours  by  over 
work  with  the  microscope — if  that  be  the  case,  I  reckon 
mine  have  the  best  of  it.  At  all  events,  I  can't  see 
how  you  can  establish  any  individual  superiority  as  to 
vision." 

At  this  moment  Prof.  Huber  had  seated  himself  at  the 
piano  and  was  entertaining  the  company  by  his  superb 
renderings  from  classical  authors.  In  reply,  I  said: 
what  you  affirm  as  to  the  eye  must  be  similarly  true  of 
the  hands.  Prof.  Huber  and  yourself  are  apparently  of 
the  same  age,  and  both  of  you  have  been  using  your 
hands  "  all  your  days."  Whence  comes  that  lightning 
rapidity  of  action;  that  wondrous  delicacy  of  touch? 
Think  you  that  the  professor  has  abused  his  muscles  by 
over  work  with  his  five  finger  exercises,  or  that  you 
have  any  claim  to  digital  superiority?  But  to  confine 
the  case  strictly  to  the  eye  alone;  how  comes  it  that  the 
mariner  can,  not  only  detect  a  "  sail  "  near  the  distant 
horizon,  but  can  also  state  with  accuracy  whether  it  be 
a  ship,  brig,  or  schooner,  and  the  direction  the  "  sail" 
may  be  pursuing,  to  all  of  which  the  passengers  present 
will  be  totally  blind? 

Noi  need  we  "  go  to  sea  "  to  find  instances  illustrative 
of  the  issue  in  hand.  The  eye  of  the  artist  recognizes, 
perforce  of  his  experience  with  the  esthetics  ot  nature, 


WORK   WITH   THE    HIGHER    "  POWERS."  239 

beauties,  to  which  that  of  the  shepherd  boy  is  innocently 
•enough  a  stranger,  and  of  the  two,  permit  me  to  inquire 
which  would  make  the  better  rnicroscopist? 

As  far  as  our  auditor  is  concerned,  we  rest  the  issue 
on  its  merits. 

A  few  years  ago  we  purchased  for  a  gentleman  well 
known  in  microscope  circles,  a  wide  apertured  objective. 
The  party  was  no  novice,  but  on  the  contrary  a  real 
hard  and  close  worker  with  the  instrument;  and  fur- 
thermore, the  gentleman  had  formerly  filled  the  chair 
•of  microscopy  in  one  of  our  most  honored  colleges. 
After  working  with  this  glass  for  about  one  year,  he 
applied  to  me  for  instruction  in  the  use  of  this  instru- 
ment, proposing  to  spend  his  vacation  with  me,  and  for 
this  purpose  the  author  was  delighted  with  the  proposal 
and  the  arrangement  was  consummated  by  unanimous 
consent.  Now  the  main  point  actuating  my  honored 
pupil  was  this :  He  had  used  his  glass  considerably — 
•enough  to  discover  that  there  were  conditions  involved 
that  he  could  not  control  as  he  desired.  Sometimes  he 
could  see  better  than  at  others;  sometimes  the  glass 
would  work  good  naturedly,  and  then  again,  at  others, 
it  wouldn't  work  well.  In  the  course  of  instruction 
which  followed,  a  slide  of  navicula  rkomboides  was  se- 
lected (this,  by  the  way,  was  a  diatom)  and  placed  on 
the  stand  for  examination  with  the  objective  named. 
In  point  of  "  difficulty"  these  shells  would  have  been 
regarded  as  average  specimens.  We  then  look  some 
little  time  to  explain  as  well  as  we  could  the  behavior 
of  the  object  glass  when  in  and  out  of  adjustment,  as 


240  HOW   TO   SEE   WITH   THE   MICROSCOPE . 

exhibited  by  the  object  selected.  Our  reason  for  mak- 
ing at  this  time  the  particular  selection  was  this :  When 
the  objective  was  in  perfect  adjustment,  the  striae  were 
admirably  well  seen  when  the  inch  ocular  was  employed,, 
but  were  assumed  to  be  invisible  under  the  two  inch. 
Next,  the  pupil  was  required  to  adjust  the  object  glass 
using  the  two-inch  ocular  only,  acting,  of  course,  under 
the  general  instructions  he  had  received.  This  done  he 
was  to  apply  the  higher  eye-piece  and  learn  of  his  suc- 
cess, practically.  Our  friend  went  at  his  task  manfully, 
and  fought  that  slide  of  diatoms  three  hours  or  more 
daily  for  more  than  a  full  week,  constantly  improving 
in  its  manipulations.  Then  it  occurred  that,  getting 
somewhat  weary  of  his  protracted  efforts  over  one  and 
the  same  slide,  he  began  to  beg  for  a  change  to  do  some- 
thing else.  Nevertheless,  he  was  put  off  time  after 
time,  until  nearly  at  the  close  of  a  long  evening's  work 
he  jumped  up  from  his  table,  and  running  towards  me, 
his  eyes  beaming  with  joy,  exclaimed,  "  I  have  it!  I 
see  it!  It's  all  plain  sailing  now!"  "Well,"  said  I> 
"what  is  it?"  He  replied,  "  I  can  see  any  shell  on  that 
slide,  I  care  not  how  small  nor  how  close  the  striae,  and 
as  well  with  the  two-inch  ocular  as  with  any  other;  and 
more  than  that,  I  can  put  the  correction  collar  right  on 
the  dot  without  humming  or  hawing,  and  do  it  every 
time."  To  this  we  responded:  "  You  have  now  solved 
your  problem,  and  are  ready  to  tackle  another  mount 
at  our  next  sitting. 

Now,  reader,  here  is  a  practical  case  in  point:  My 
pupil  had  not  only  been  improving  himself  in  the  "hand- 


WORK   WITH   THE    HIGHER     "POWERS."  241 

ling  "  of  the  object  glass,  but  all  this  time  his  eye  was 
becoming  educated.  At  the  commencement  it  would 
have  been  an  utter  impossibility  for  him  to  have  recog- 
nized the  striae  of  the  rhomboides  with  but  the  two- 
inch  eye-piece,  nevertheless  the  writer  saw  them  splen- 
didly, and  with  that  exquisite  definition  which  per- 
tains only  to  the  work  of  these  high-angled  glasses. 
Had  1  told  my  pupil  this  at  the  start,  he  would  proba- 
bly have  received  the  assertion  in  a  becoming  manner, 
meanwhile  entertaining  some  "  first  class  doubts  "  under 
his  sleeve;"  full  fledged  doubts,  too,  and  simply  wait- 
ing for  a  fine  day  to  fly. 

Place  the  microscope  in  the  hands  of  the  shepherd 
boy ;  its  total  defeat  is  established.  Adjust,  if  you  will, 
The  objective  with  the  utmost  nicety,  and  arrange  the 
illumination  to  perfection,  and  total  defeat  still  reigns 
tiiumphant.  He  neither  has  the  capacity  of  seeing  well 
nor  of  judging  well  of  what  may  be  seen,  neverthe- 
less, he  can  honestly  and  innocently  look  you  squarely 
in  the  face  and  assert  that  he  has  as  good  a  pair  of  eyes 
«'  as  the  next  man." 

We  have  thus  taken  some  little  pains,  and  hope  not 
without  profit  to  the  reader,  to  establish  a  fact  well 
knwn  to  all  who  are  expert  in  the  use  of  the  microscope. 
If  our  views  are  correct,  it  obtains  that  no  inconsider- 
able amount  of  time  and  patient  care  and  study  are  each 
individual  elements  in  the  outlay  necessary  in  the  effort 
to  become  an  accomplished  observer,  and  if  this  is  to  be 
considered  in  the  light  of  an  evil,  then  let  it  be  remem- 
bered that  "  there  are  no  evils  unless  attended  with 

Microscopy  16 


242  HOW  TO   SEE   WITH   THE   MICROSCOPE. 

some  corresponding  good."  And  fortunate  it  is,  in  the 
case  before  us,  there  is  a  fascination  accompanying  the 
intelligent  use  of  the  microscope  knowing  neither  limit 
nor  bounds,  and  the  task  of  becoming  well  acquainted 
with  the  use  of  the  instrument  is  merely  a  labor  of  love. 
There  is  another  aspect  of  the  matter  which  deserves  a 
word  or  two,  to  wit:  The  popular  idea  with  many  is, 
that  if  there  be  a  certain  amount  of  eye  training  essen- 
tial in  the  use  of  the  "  high  powers,"  this  has  no  appli- 
cation to  those  who  use  the  lower  amplifications.  Says 
one,  "  you  are  all  right  about  your  ey^  education  when 
there  is  such  nice  work  as  showing  the  19th  band  in 
hand ;  but  then  you  see  most  of  my  work  is  done  with 
the  inch,  and  that's  quite  another  thing."  Now  there 
is  just  as  much  error  here,  but  it  is  of  a  less  serious 
character.  The  truth  is,  the  expert  can  see  more  with 
the  inch,  and  by  the  "expert"  I  mean  (for  the  time 
being)  those  referred  to  who  are  able  to  display  hand- 
somely such  tests  as  the  19th  band.  Every  day  expe- 
rience with  pupils  in  the  laboratory  demonstrate  this 
fact  pointedly.  Thus:  At  the  commencement  of  his 
practice,  the  novice  is  quite  content  with  the  meanest 
French  triplet  the  premises  afford,  but  in  less  than  a 
month  he  will  hold  it  in  perfect  contempt,  and  his  sub- 
sequent progress  will  to  a  great  extent  be  properly 
measured  or  indexed  by  the  constantly  increasing  capa- 
city to  handle  even  these  non-adjusting  glasses. 

In  thus  insisting  on  the  necessity  of  the  proper  edu- 
cation of  the  eye,  let  us  look  for  a  moment  to  its  im- 
portant bearing  on  a  particular  class  of  observations. 


WORK   WITH   THE   HIGHER     "  POWERS."  243 

We  intended  to  refer  to  this  bye-and-bye,  but  it  finds 
an  appropriate  place  right  here.  We  may,  however, 
refer  to  it  at  some  future  time.  I  allude  to  that  class 
of  work  intimately  connected  with  the  use  of  object 
glasses  of  wide  apertures,  and  over  exceedingly  difficult 
lined  structures;  for  instance, 'the  display  of  the  stride 
of  amphipleura  pellucida.  But  let  the  reader  remember 
that  this  class  of  work  is  not  confined  to  the  study  of 
diatoms. 

To  illustrate  what  we  have  in  hand,  reference  is  made 
to  the  following  sketch :  Let  C-D  and  G-H  be  a  sec- 
tional view  of  some  "  difficult "  diatom,  such  as  amphr 
pleura  pellucida  or  the  like,  the  short  lines  1,  2,  3,  4? 
etc.,  representing  in  section  the  elevations  of  the  striae; 
M  and  N  being  views  "  in  plan"  as  seen  conditionally 
in  the  microscope.  Let  us  first  consider  the  effect  of 
illuminating  C-D  with  direct  central  light,  as  indicated 
by  the  line  A-B.  The  effect  will  be  as  shown  in  plan 
at  N,  to  wit :  There  will  appear  but  a  series  of  exceed- 
ingly fine  lines;  so  fine  (mark  the  words,  not  necessa- 
rily close)  that  it  will  be  impossible  to  see  them  with 
any  glass  extant.  Recourse  must  then  be  had  to  "  ob- 
lique illumination."  Now  let  C-D,  as  duplicated  at 
G-H,  be  illuminated  by  the  oblique  beam  E-F.  The 
effect  of  this  is  shown  in  section  at  1',  2',  3',  etc.,  and 
in  plan  at  K,  where  we  have  the  view  as  displayed  in 
the  microscope.  Here  we  have  tAVO  things  successfully 
accomplished;  the  strise  which  in  the  former  case  were 
so  "  fine  "  as  to  be  invisible  have  now  become  broad  and 
can  easily  be  distinguished  by  the  eye ;  and,  secondly, 


244 


WORK   WITH   THE    HIGHER     "  POWERS."  245 

this  last  display  is  as  false,  as  to  many  it  has  been  ac- 
ceptable. Now  let  down  the  obliquity  of  the  illumina- 
tion, as  indicated  by  the  line  I-J;  the  effect  is  noted  on 
the  sketch  at  L,  and  with  a  first  class  high  balsam  angled 
objective  and  an  eye  well  trained,  it  may  be  that  the 
striae  are  not  only  discernable  in  the  microscope,  but  the 
observer  will  further  be  able  to  note  the  intervening 
spaces  also;  and  this,  too,  which  the  certain  knowledge 
that  of  the  varying  condition  set  forth,  the  latter  dis- 
play is  not  only  the  most  satisfactory  in  general  terms, 
but  the  most  truthful.  It  is  also  apparent  that  the 
more  we  decrease  the  angle  of  the  illuminating  beam 
the  louder  the  call  on'  the  defining  power  of  the  object 
glass  and  the  greater  the  demand  for  education  on  the 
part  of  the  eye.  In  other  words,  the  expert,  all  other 
things  being  equal,  with  a  pair  of  eyes  trained  by  long 
practice  in  his  profession,  has  the  better  chance  of  see- 
ing things  as  they  actually  are.  From  the  illustration 
given  we  deduce  several  propositions,  viz: 

First,  it  is  always  better  to  see  structure  somehow 
than  not  at  all.  Let  those  addicted  solely  to  the  use 
of  narrow  apertures  ponder  this  well. 

Secondly,  when  engaged  in  investigations  of  "  diffi- 
cult" structure  similar  to  the  case  presented,  and  calling 
at  the  best  for  light  of  considerable  obliquity,  the  less 
of  the  obliquity,  as  a  rule,  and  within  certain  limits,  the 
better ;  and  the  more  perfect  the  education  of  the  eye 
the  less  will  be  the  call  above  mentioned. 

Third,  the  higher  the  balsam  angle  of  the  glass  the 
LESS  will  be  the  obliquity  required.  Let  those  who 


246  HOW   TO   SEE    WITH   THE    MICROSCOPE. 

favor  work  with  centrally  disposed  light  make  a  note 
ol  this. 

Says  one  (alluding  to  the  second  proposition),  I  don't 
exactly  see  that  thing  as  you  do.  Suppose,  for  instance, 
that  the  objective  and  the  eye  were  both  so  perfect  as 
to  allow  the  illumination  to  become  axial,  as  in  your 
first  illustration,  wouldn't  that  be  better  still? 

We  reply,  ask  the  artist  if  he  would  prefer  the  land- 
scape thus  lighted.  The  architect  of  the  universe  ex- 
pressly arranged  ^things  to  prevent  such  a  catastrophe. 
A  certain  amount  of  shade  is  as  necessary  as  that  of 
light.  Such  a  thing  as  "  dead  central  illumination," 
although  often  talked  about,  is  a  myth. 

Feeling  deeply  the  importance  of  calling  the  atten- 
tion of  the  reader  to  an  element  which  we  regard  as  of 

O 

vital  importance,  we  have  accordingly  done  so  at  the 
risk  of  being  somewhat  tedious. 

POSITION  OF  OBSERVER. 

Our  experience  is,  that  in  sixty  cases  out  of  the  hun- 
dred, having  made  some  preliminary  examination  of  an 
object  under  study,  and  thus  demonstrating  the  neces- 
sity of  the  use  of  higher  amplifications,  that  with  the 
latter  comes  also  the  necessity  of  a  long  and  protracted 
sitting ;  in  fact  a  downright  seige  is  inaugurated.  It  is 
better  in  all  such  cases  to  postpone  work  until  evening, 
or  at  least  so  to  arrange  that  the  observer  shall  have 
perfect  immunity  trom  interruptions  of  any  nature; 
and  at  the  commencement  of  such  work  it  is  of  para- 
mount importance  that  the  operator  adopt  such  a  posi- 


PO6ITIO^     OF   OBSERVER.  247 

tion  at  the  work  table  as  will  allow  him  to  observe  for 
hours  without  serious  fatigue.  Such  a  table  as  has 
already  been  recommended,  with  two  front  drawers, 
will  be  just  what  is  wanted.  The  novice  is  here  re- 
minded that  in  working  with  the  higher  powers,  after 
having  placed  the  object  in  position  under  the  objective, 
the  latter  being  correctly  adjusted,  there  will  be  no 
longer  use  for  the  coarse  adjustment.  Having,  then, 
our  table,  place  the  chair  adjacent  thereto,  but  in  place 
of  putting  its  front  edge  parallel  to  the  front  of  the 
table,  as  is  generally  done,  turn  the  chair  to  the  right 
until  the  front  and  left-hand  sides  form  equal  angles 
with  the  front  of  the  table,  the  angular  point  formed 
by  the  meeting  of  the  front  and  left-hand  edges  of  the 
chair  being  adjacent  to  the  table.  Now  let  the  observer 
seat  himself,  placing  the  shank  of  the  left  shoe  on  the 
left-hand  round  of  the  chair.  Pull  out  both  drawers, 
so  that  the  edge  of  these,  assisted  by  the  edge  of  the 
table,  shall  form  a  double  rest  for  the  forearm.  Now 
place  the  stand  in  such  a  position,  that  is,  with  refer- 
ence to  the  front  of  the  table,  that  the  left  hand  finds 
its  way  easily  to  the  fine  adjustment,  while  that  of  the 
right  grasps  the  mirror  bodily,  the  tube  being  mean- 
while adjusted  to  the  standard  length,  and  the  whole 
instrument  properly  inclined.  Let  the  reader  practice 
these  directions  thoroughly  until  he  shall  be  able  to 
thus  sit  at  his  instrument  firmly  wedged  to  it.  It  will  be 
noticed  that,  once  in  this  position,  either  hand  can  grasp 
the  object  slide  for  the  purpose  of  making  any  neces- 
sary change,  and  without  seriously  disturbing  the  double 


248  HOW   TO    SEE    WITH   THE    MICROSCOPE. 

adjustment  for  the  forearm,  while  the  right  hand,  being 
thus  so  nicely  supported,  is  enabled  to  manipulate  the 
mirror  with  almost  mathematical  precision.  At  the 
first,  as  might  easily  be  supposed,  the  sharp  edges  of  the 
table  and  drawers  will  be  a  source  of  some  little  incon- 
venience. This  can  be  remedied  by  placing  a  pair  of 
napkins  thereon;  but  the  better  way  is  to  endure  this 
slight  annoyance  for  a  little  time,  when  the  forearm 
will  be  found  to  have  adapted  itself  to  the  situation. 
The  position  thus  described  we  have  represented  as  far 
as  possible  in  the  frontispiece,  using  such  furniture  as 
was  at  hand  in  the  photographer's  gallery 

This  pose  can  be  varied  at  times  by  bringing  the  left 
knee  in  use  so  that  it  may  support  the  left  elbow.  Thus 
we  get  three  rests  tor  the  left  arm,  and  sometimes  we 
get  the  shank  of  the  right  foot  on  to  the  front  round 
of  the  chair,  spreading  the  knee  open  a  bit  and  wedging 
it  under  the  right  hand  draw.  Other  little  changes  are 

o  o 

practicable  and  need  not  be  detailed  here. 

Of  all  the  manipulations  connected  with  the  use  of 
the  higher  powers,  the  adjustment  ot  the  objective  (sup- 
posing, of  course,  that  it  is  a  good  one,  one  that  will 
respond  to  the  collar  adjustment),  is  of  pa/ramount  im- 
portance. For  reasons  previously  stated,  two  elements 
are  involved,  namely,  the  behavior  of  the  object  glass 
and  the  education  of  the  eye ;  and  here  the  use  of  the 
diatommecaB  is  imperative.  We  have  insisted  on  this 
for  years.  These  little  organisms  are  the  most  con- 
venient, and  then,  again,  any  little  deviation  from  the 
perfect  correction  of  the  objective  is  sure  to  "  stick  out " 


POSITION    OF   OBSERVER.  249 

;and  be  detected.  This  is  not  the  case  with  other  objects. 
Show  the  tyro  a  scale  of  podurae  under  a  tolerably  nar- 
row angled  one-tenth,  and  likewise  display  the  same 
with  a  similar  object  glass  of  the  higher  balsam  angles. 
There  will  be  as  much  difference  in  the  quality  of  the 
two  exhibits  as  there  is  (I  was  going  to  say)  between 
light  and  total  darkness ;  and  yet,  nevertheless,  the  nov- 
ice will  be  as  well  satisfied  with  the  one  as  with  the 
other;  but  let  the  experiment  be  repeated,  using  in  the 
place  of  the  podura  a  balsam  mount  of  surriella  gemma, 
both  glasses  doing  their  best,  as  before,  and  the  tyro  is 
no  longer  "  at  sea  "  as  to  his  choice.  Moreover,  at  this 
stage  of  his  experience  he  will  be  fully  prepared  to  blow 
his  trumpet  in  the  support  of  one  of  the  most  absurd 
and  stupid  errors  that  has  ever  been  promulgated  since 
the  time  of  Adam,  to  wit,  "  High  angled  glasses  are  only 
fit  for  work  over  diatoms ! ! " 

When  we  say  that  diatoms  are  the  most  convenient 
objects  over  which  to  study  the  adjustment  of  the  ob- 
jective, we  mean  it,  and  thereto  attaches  greater  force 
than  the  casual  reader  may  suppose.  If  it  be  imagined 
that  these  objects  are  "  convenient"  because  their  gen- 
eral proportions  are  about  the  thing — because  they  can 
be  purchased  at  slight  expense,  or,  if  preferred,  pre- 
pared by  the  observer  himself,  or  even  be  it  granted 
that  the  markings  on  the  more  difficult  of  these  shells 
will  only  surrender  to  a  first-class  objective  in  perfect 
adjustment,  we  admit  the  facts,  but  the  story  is  not 
fully  told. 

The  grand,  the  culminating  convenience  attending 


250  HOW  TO   SEE   WITH   THE   MICROSCOPE. 

the  use  of  diatoms  in  the  study  of  the  objectives  used 
under  high  amplifications,  is  this :  We  are  enabled  to- 
display  on  one  and  the  same  mount,  shells  of  the  same 
family  and  species,  differing  only  in  size,  and  we  thu^ 
are  on  the  instant  ready  to  study  the  work  of  the  ob- 
jective over  each.  Now  if  it  so  be,  and  we  make  it  a 
point  that  it  shall  so  be  that  the  smaller  shell  is  in  all 
respects  the  more  difficult  of  the  two.  Then  it  occurs- 
that  the  student,  having  mastered  such  smaller  frustule 
can  examine  at  his  leisure  the  larger  ones,  and  with  the 
certainty  that  his  objective  is  in  at  least  approximate 
adjustment;  hence  he  is  further  prepared  to  note  the 
difference  in  the  behavior  of  the  object  glass  over  the 
different  diatoms,  and  thus  he  arrives  at  items  of  the 
utmost  value;  all  this,  too, ^without  any  change  of  the 
mount. 

Still  other  conveniences  there  are  attending  the  use 
of  the  diatom,  their  extreme  thinness  preventing  the 
shadow  of  one  shell  from  interfering  with  the  defini- 
tion of  another,  thus  getting  rid  of  a  complication 
which  would  prove  of  serious  detriment  in  the  early 
studies  of  the  student,  while  by  and  by  he  can  essay  ai> 
attack  on  the  very  problem  named  by  merely  selecting 
sueh  positions  of  the  amount  as  contain  the  little 
organisms  huddled  together.  Thus  learning  their  char- 
acter and  being  thus  forewarned,  is  fore-armed  against 
the  time  when  he  shall  be  brought  in  contact  with 
other  slides  presenting  the  same  difficulty,  but  in  a 
more  determined  manner. 

But  let  the  reader  note  this  fact.     It  is  one  thing  to 


POSITION    OF    OBSERVER.  251 

look  at  diatoms,  and  quite  another  to  study  them  with 
the  especial  object  of  becoming  acquainted  with  the 
behavior  of  the  objective,  while  it  must  be  admitted 
that  there  is  a  fascination  and  charm  per  se9  connected 
with  diatom  examinations  under  the  microscope.  It  is- 
equ.dly  true  that  the  student  can  use  them  legitimately 
and  for  the  purpose  named,  without  establishing  any 
claim  to  the  functions  of  the  diatomist. 

Referring  to  the  especial  purposes  we  have  been  con- 
sidering, the  following  list  of  objects  will  amply  suffice, 
for  the  study  of  the  one-sixth  or  one-tenth  objectives,, 
viz: 

1.  Navicular  Rhomboides,  Monmouth,  Maine,  Balsam  Mount 

2.  Navicular  Rhomboides,  Cherryfleld,  Balsam  Mount. 

3.  Erustulia  Saxonica,  Leipsig,  Germany,  Balsam  Mount. 

4.  Frustulia  Saxonica,  Isle  of  Shoals,  U.  S.,  Balsam  Mount. 

5.  Amphipleura  Pellucida,  Bridge  of  Allan,  Scotland,  Balsam 

Mount. 

6.  Amphipleura  Pellucida,  Aberdeen,  Scotland,  Balsam  Mount. 

7.  Surriella  Gemma,  Balsam  Mount. 

Of  the  above  list,  Nos.  1  and  2  can  readily  be  ob- 
tained of  the  dealers.  As  to  the  others  named,  Prof. 
H.  L.  Smith,  of  Geneva, .N.  Y.,  has  a  large  supply  of 
the  material,  and  has  kindly  supplied  the  author  and 
his  friends  with  excellent  mounts  and  at  figures  much 
below  the  usual  list  prices. 

In  addition  to  the  diatoms,  a  genuine  mount  of 
English  podura  will  be  a  capital  thing  to  have  on  hand 
for  occasional  comparisons,  but  the  student  must  on  no- 
account  select  the  slide  himself.  Poor  scales  are  simply 
good  for  nothing,  while  perfect  ones  are  held  by  the 
opticians  in  the  highest  esteem,  and  are  constantly  used 


252  HOW   TO   SEE   WITH   THE   MICROSCOPE. 

by  them  in  the  final  corrections  of  the  objective.  Of 
all  the  scales  of  podura  we  have  yet  seen,  a  mount  was 
shown  us  last  summer  by  Mr.  Herbert  Spencer,  which 
was  perfection  itself.  As  an  index  ot  the  value  Mr. 
Spencer  attached  to  this  mount,  I  will  add  that  he  had 
once  offered  one  of  his  first  class  one-tenth  objectives 
in  exchange  for  it  I 

Every  microscopist  needs  a  suitable  stage  micrometer 
and  very  few  have  reliable  ones.  We  gladly  state  that 
Prof.  W.  A.  Rogers,  of  Cambridge,  Mass.,  has  after 
years  of  careful  study  succeeded  in  making  rulings  on 
glass  rivaling  if  not  excelling  those  of  Noberl  himself. 
Not  long  since  Prof.  Rogers  ruled  for  us  a  plate,  con- 
taining lines  100,  1,000,  2,000,  5,000,  10,000,  20,000, 
40,000  and  80,000  to  the  inch,  which  was  a  marvel  in 
point  of  accuracy  and  delicacy.  Subsequently  Prof. 
Rogers  ruled  a  plate  for  us  up  to  120,000  lines  to  the 
inch.  This  band  the  author  has  seen  well  and  has 
shown  to  his  friends.  We  therefore  recommend  first, 
that  every  student  should  be  possessed  of  a  micrometer ; 
and  secondly,  that  the  same  be  procured  from  Prof. 
Rogers.  It  will  be  well  while  one  is  about  it,  to  order 
a  plate  ruled  as  high  as  80,000  to  the  inch,  inasmuch  as 
the  cost  is  not  materially  enhanced,  the  plate  will  thus 
do  double  service  not  only  as  a  stage  micrometer,  but 
as  a  test  plate  for  the  comparison  and  study  of  objec- 
tives. In  this  connection  the  reader  will  remember 
that  we  have  advised  that  eye-piece  micrometers  be 
ruled  600  lines  to  the  inch.  Hence,  if  our  advice  is 
followed,  let  the  stage  micrometer  have  a  similar  band. 


POSITION    OF   OBSERVER.  253 

The  positive  convenience  resulting  from  this  in  the 
measurement  of  the  focal  length  of  objectives  by  the 
method  previously  described  is  too  obvious  to  need 
further  comment. 

The  series  of  graduated  diatoms  by  Moller  of  Wedel, 
Germany,  and  generally  known  as  the  Moller  test 
Plate,  is  now  to  be  found  in  the  cabinet  of  nearly 
every  uiicroscopist,  and  can  be  advantageously  supple- 
mented to  the  list  above  given.  A  table  showing  the 
mean  of  the  measurement  of  ten  of  these  plates  will 
be  now  furnished  and  thus  the  plate  can  on  a  pinch  be 
made  to  do  approximate  duty  as  a  stage  micrometer. 

MEAN  OF  TEN  MEASUREMENTS  OF  MOLLER  TEST  PLATES,. 
BY  PROF.  E.  W.  MORELEY,  M.  D.,  OF  HUDSON,  OHIO. 

1.  Triceratium  Favus 3.1to   4. 

2.  Pinnularia  Nobilis 11.7  to  14. 

3.  Navicula  Lyra , 14.5  to  18. 

4.  Navicula  Lyra 23.0  to  30.5. 

5.  Pinnularia  Interrupta 25.5  to  29.5. 

6.  Stauronesis  Phoemcenteron 31.    to  36.5. 

7.  Grammatophora  Marina 36.    to  39. 

8.  Pleurosigma  Balticum 32.    to  37. 

9.  Pleurosigma  Acurninatum 41.    to  46.5. 

10.  Nitzschia  Amphoyx 43.  to  49. 

11.  Pleurosigma  Angulatum 44.  to  49. 

12.  Grammatophora  Oceanica=G.  Subtilissima 60.  to  67. 

13.  Surriella  Gemma 43.  to  54. 

14.  Nitzschia  Sigmoidea 61.  to  64. 

15.  Pleurosigma  Fasciola 55.  to  58. 

16.  Surriella  Gemma.    Longitudinal 64.  to  69. 

17.  Cymatopleura  Elliptica 55.  to  81. 

18.  Navicula  Crassinervis,  Frustulia  Saxonica 78.  to  87. 

19.  Nitzschia  Curvula 83.  to  90. 

20.  Amphipleura  Pellucida 92.  to  95. 


254  HOW  TO   SEE   WITH   THE   MICROSCOPE. 


THESE   FIGURES  DENOTING  THE   NUMBER  OF  LINES  IN  .001 
OF   AN   ENGLISH   INCH. 

As  a  matter  of  convenience  to  those  having  the  cele- 
brated Nobert  19  band  test  plate,  we  present  the  fol- 
lowing tabulated  values  of  the  rulings.  The  first 
column  contains  the  value  in  Paris  lines.  The  second 
the  number  c  f  lines  in  .001  of  an  English  inch,  as  ruled 
in  the  several  bands. 


NUMBER.                                  PARIS  LINES.                                  IN  .100  ENO.  IN. 
1 1,000 11.26 

2 1,500 16.89 

3 2,000 22.52 

4 2,500 28.13 

5 3,000 33.78 

6 3,500 39.41 

7 4,000 45.04 

8 4,500.... 50.67 

9 5,000 56.30 

10 5,f>00 61.93 

11 6.000 67.56 

12 6.500 73.19 

13 7.000 78.82 

14 7,500 84.45 

15 8,000 90.08 

16 8,500 95.71 

17 3,000 101.34 

18 9,500 106.97 

19 10,000 112.60 

Returning  now  to  our  original  list  of  diatom  mounts 
we  proceed  to  give  such  a  description  of  the  same  as 
will  enable  the  student  to  approach  them  intelligently, 
iind  without  undue  loss  or  waste  of  time.  The  first  two 
slides  are  pretty  much  the  same  thing,  both  contain 


POSITION    OF    OBSERVER.  255 

tine  shells  of  navicular  rhomboides,  and  nicely  assorted 
as  to  size  and  "difficulty."  The  larger,  or  even  the 
medium  sized  shells  are  easily  displayed  (we  refer  to 
the  transverse  striae)  by  such  a  glass  as  the  Spencer  dry 
•one-fourth  of  115°,  when  nicely  adjusted,  while  the 
smaller  frustules  are  more  "difficult"  than  the  No.  18 
of  the  Moller  plate.  These  mounts  are  therfore  valu- 
able on  account  of  their  range,  and  the  reader  has 
.already  our  reasons  governing  the  selection  thereof. 
When  these  slides  are  thoroughly  mastered,  the  student 
will  be  ready  to  attack  the  Saxonica  from  Leipsig. 
These  vary  also,  a  medium  shell  being  about  as  obsti- 
nate as  the  No.  18  of  the  Moller  plate,  and  will  defeat 
the  Spencer  one-fourth.  The  Saxonica  from  the  Isle 
•of  Shoals  is  still  more  bothersome.  These  frustules 
are  very  small  i  nd  very  thin,  and  at  the  start  the 
.student  should  select  the  very  largest  and  most  vigorous 
shell  he  can  find  on  the  mount,  proceeding  carefully  as 
he  may  acquire  skill,  to  the  smaller  ones,  and  before  he 
•can  establish  any  claim  to  have  mastered  this  slide  he 
must  be  able  to  show  the  very  smallest  and  thinnest 
shell  acceptably.  In  point  of  "difficulty"  these  smaller 
diatoms  rival  the  No.  19  of  the  Moller  plate,  while  the 
.smallest  and  the  very  thinnest  are  a  fair  match  for  the 
No.  20.  Of  the  amphipleuras,  that  from  the  "  Bridge 
of  Allan,"  Scotland,  is  the  easier  of  the  two,  and 
should  be  studied  first.  This  slide  in  common  with  the 
two  last  mentioned  calls  for  object-glasses  of  high 
apertures.  To  attack  them  with  any  of  the  low  angled 
glasses  is  but  a  waste  of  time  and  patience.  The  mount 


256  HOW   TO    SEE   WITH   THE    MICROSCOPE. 

of  surriella  gemma  is  selected  for  reasons  very  much 
akin  to  the  mention  that  has  been  made  of  podura. 
These  shells  are  not  suited  for  the  purpose  of  study, 
but  are  admirably  adapted  for  comparisons.  The 
actual  structure  of  this  diatom  is  yet  a  matter  sub 
judice. 

Now  let  us  go  back  again  to  the  first  mounts  named 
in  the  list.  We  have  had  occasion  before  to  assert  that 
one  of  the  advantages  resulting  from  the  study  of  di- 
atoms is  due  to  the  fact  that  the  student  in  mastering 
one  of  the  smaller  and  more  difficult  ones  becomes 
fortified  as  to  the  adjustment  of  his  glass.  Supposing 
then  that  by  some  good  luck  he  has  succeeded  in  dis- 
playing the  smaller  frustules  of  the  Monmouth  or 
Cherry  field.  He  can  return  to  the  larger  shells  with 
tolerable  assurance  that  his  glass  is  in  fair  correction. 
But  mark  this.  In  order  to  show  the  little  fellows, 
there  was  need  of  greater  obliquity  of  illumination, 
which,  when  return  shall  be  made  to  the  larger  shells 
can  profitably  be  dispensed  with.  Now  although  the 
slide  of  diatoms  offer  special  conveniences,  let  the 
student  adopt  this  line  of  study,  no  matter  what  may 
be  the  character  of  the  object  under  his  objective,  select- 
ing the  most  obscure  and  diaphanous  structure  possi- 
ble to  bring  into  the  field,  and  making  sure  that  there 
is  a  sufficiency  of  oblique  illumination. 

From  what  has  been  said  it  may  be  adduced  as  a  gen- 
eral rule  that  it  is  advisable  to  study  the  corrections  of 
the  objective  by  the  aid  of  oblique  light,  and  over  the 
finest  structure  the  mount  can  be  made  to  exhibit,  and 


POSITION   OF    OBSERVEH.  257 

to  the  beginner  no  better  advice  can  be  given.  It  is 
simply  impossible  for  the  novice  to  study  the  correc- 
tions of  a  high  angled  object-glass  by  centrally  disposed 
illumination. 

In  the  selection  of  the  ohjects  recommended  to  the 
student,  we  have  been  governed  by  these  and  similar 
considerations.  All  of  the  slides  named  contain  frus- 
tules  requiring  the  use  of  light  at  least  40°  from  axisr 
and  the  student  will  in  his  first  attempts  be  compelled 
to  go  considerably  higher  than  that  figure.  The  exact 
amount  of  obliquity  essential  to  the  best  display  he  can 
possibly  make,  will  depend  on  his  object-glass  the  cor- 
rectness of  its  adjustment,  and  the  education  of  his 
eye. 

We  shall,  on  some  succeeding  page  have  a  few  words 
to  say  as  to  the  management,  etc.,  of  high  balsam 
apertures  by  centrally  disposed  light.  With  this  one 
exception  only,  anything  that  we  may  have  to  offer  in 
the  way  of  instruction  bearing  on  the  use  of  these 
glasses  will  be  confined  to  the  study  of  the  diatoms 
which  have  been  presented.  The  student  who  can 
properly  display  the  seven  mounts  to  which  his  atten- 
tion has  been  invited,  together  with  the  Moller  plate 
and  the  podura,  can  safely  be  allowed  to  shift  for  him- 
self. We,  however,  fear  that  our  ability  to  teach  this 
much  will  not  now  keep  pace  with  our  sincere  desire. 
Competent,  or  incompetent,  we  propose  to  try.  A 
singular  fact  it  is,  that  among  all  the  works  thus  far 
written  on  the  microscope  not  one  word  of  instruction 
can  be  found  as  to  the  management  of  objectives  of 

Microscopy  17 


258  HOW   TO    SEE   WITH   THE   MICROSCOPE. 

wide  apertures.  It  is  therefore  high  time  that  some 
•one  k<  assume  the  judicial."  Any  endeavor  on  the  part 
of  anyone  to  teach  the  management  of  wide  apertured 
object-glasses  must  in  the  nature  of  things  be  incom- 
plete, and  at  the  best  but  approximative.  Notably  so 
as  to  written  instructions,  no  two  objectives  work 
exactly  alike,  and  appearances  in  the  field  will  be  mod- 
ified by  the  individual  corrections  of  the  particular 
glass  employed.  Of  two  objectives,  one  may  be  supe- 
rior to  the  other.  Hence  the  student  not  being  a  con- 
noisseur becomes  environed  with  doubts  that  the  ex- 
pert might  easily  cause  to  vanish  by  a  little  personal 
interference.  Object-glasses,  too,  wcrk  differently  over 
different  objects.  The  appearance  of  a  dry  mounted 
object  is  characteristically  at  variance  with  the  appear- 
ances presented  by  balsam  mounts,  and  here  is  our 
reason  for  selecting  in  every  instance  the  latter  for  the 
instruction  of  the  beginner.  Neither  is  it  possible  for 
the  professional  philologist  by  mere  force  of  word  pic- 
turing to  convey  to  the  mind  of  the  learner  just  what 
may  be  desired.  And  even  should  the  teacher  be  fortu- 
nate enough  to  employ  the  most  accurate  descriptions 
language  can  afford,  then  he  has  no  assurance  of  being 
perfectly  understood  by  the  pupil.  The  author  being 
no  philologist,  and  having  but  a  little  command  of 
language  desirous  of  using  none  other  than  the  simplest 
words,  thus  adapting  this  little  book  to  the  compre- 
hension of  all,  can  but  essay  his  best  and  only  hope  for 
partial  success. 

A  word  or  two  further  before  we  proceed  with  our 


POSITION    OF    OBSERVER.  259 

tuition.  The  remark  is  often  of  late  made,  "what  does 
all  this  talk  about  the  handling  "  of  objectives  mean? 
Are  we  to  understand  that  the  real  work  of  the  micro- 
scopist consists  in  the  resolution  of  a  few  diatoms,  or 
the  exhibition  of  the  rulings  of  the  19thNobert  band? 
To  this  we  reply,  that  all  this  is  implied  and  a  very 
great  deal  more ;  it  means  that  the  microscopist  shall 
know  as  much  of  the  microscope  as  it  is  expected  of 
the  engineer  to  know  of  his  level  or  transit.  In 

O 

geodesy  the  value  of  entire  systems  of  costly  triangu- 
lations  are  wholly  dependent  on  the  accuracy  of  the 
original  base  line,  and  in  a  similar  manner  is  the  work 
of  the  microscopist  affected.  We  often  hear  old  ob- 
servers claim  that  all  work  worth  having  with  the 
microscope  is  accomplished  with  amplifications  less  than 
300  diameters ;  and  then  again  the  scientific  contribu- 
tions resulting  from  the  use  of  the  finest  English  objec- 
tives in  the  hands  of  physicists  like  Professors  Tyndall 
and  Huxley  dependent  on  amplifications  of  5,000  and 
6,000  diameters,  have  been  seriously  called  in  question, 
yea,  disputed  by  those  working  with  objectives  not 
worth  the  weight  of  their  brass  mountings!  We 
repeat,  that  it  is  eminently  the  business  of  the  would- 
be  microscopist  to  know  all  that  can  be  known  of  his 
instrument ;  if,  when  he  has  to  an  acceptable  extent  ac- 
quired this  knowledge,  if  so  be  that  he  prefers  not  to 
devote  his  time  and  microscope  to  investigation,  he  has 
the  satisfaction  of  being  conscious  that  what  was  done 
was  well  done.  Had  the  engineers  employed  in  meas- 
uring the  original  base  on  which  the  coast  survey  was 


260  HOW   TO    SEE   WITH   THE    MICROSCOPE. 

founded,  chosen  to  have  abandoned  the  work  on  the 
completion  of  the  base,  there  would  have  been  no  time 
lost  or  wasted ;  per  contra,  had  the  base  been  but  im- 
perfectly measured,  and  the  engineers  proceeded  to 
build  the  other  triangles  resting  thereon,  they  would 
not  long  have  continued  in  the  service,  but  would  have 
been  furnished  with  palpable  reasons  for  leaving! 

Again,  the  question  is  ofttimes  asked,  do  you  require 
that  the  observer  shall  be  familiar  enough  with  his  ob- 
jective as  to  work  it  up  to  the  same  force  as  its  maker 
could?  Its  the  legitimate  business  of  the  optician,  and 
he  can  thus  afford  to  spend  his  time  on  a  matter  which 
to  him  is  a  necessity,  but  to  demand  this  much  of  the 
practical  observer  seems  uncalled  for.  In  answer  to 
this  oft-repeated  remark,  we  wish  it  distinctly  under- 
stood that  it  is  eminently  the  business  of  the  observer 
to  fully  understand  the  practical  woiking  of  his  objec- 
tives. The  man  who  cannot  make  his  object-glass  per- 
form as  well  as  when  in  the  hands  of  its  maker,  is  using 
an  instrument  that  he  does  not  fully  understand,  of 
which  the  fact  becomes  incontestible  proof.  If  it  be 
necessary  that  the  optician  be  able  to  work  an  objec- 
tive to  its  maximum,  it  is  imperative  that  the  micro- 
scopist  should  do  as  much.  Until  this  shall  be  the 
case,  absurdities  will  abound.  Take  for  instance  a  con- 
dition that  often  occurs.  The  microscopist  orders  a 
new  objective  from  the  optician.  The  specifications  are 
complete,  and  the  glass  is  made  conformably  thereto. 
In  due  time  the  purchaser  receives  his  glass,  and  can  do 
nothing  with  it,  and  it  is  returned  in  high  dungeon  to 


POSITION    OF   OBSERVES.  261 

its  maker.  And  why?  Simply  because  the  purchaser 
was  as  incompetent  to  "  handle  "  the  instrument,  as 
perchance  he  might  have  been  to  manipulate  a  piano- 
forte or  church  organ.  And  then  again  through  his 
ignorance  he  might  have  possibly  ordered  the  very 
glass  he  did  not  want.  What  would  we  say  to  the 
invalid  who  on  summoning  the  attendance  of  the  physi- 
cian should  undertake  to  dictate  as  to  the  treatment! 

Again,  we  have  often  been  requested  b}'  our  friends 
and  visitors  to  examine  objectives  and  give  our  opinion 
thereon ;  and,  as  a  rule,  five  minutes  Avill  suffice  for  this. 
But,  says  the  owner,  "you  must  be  prejudiced  against 
my  glass.  No  man  could  give  a  well  grounded  opinion 
in  the  few  moments  you  have  occupied."  Nevertheless, 
we  have  given  hundreds  of  just  such  opinions  without 
having  had  occasion  to  modify  or  retract,  and  here  is 
an  illustration  showing  that  time  spent  in  the  study  of 
objectives  is  neither  totally  lost  nor  without  its  compen- 
sations. We  reiterate,  let  the  microscopist  understand 
well  his  tools,  and  in  the  hope  of  being  at  least  some 
assistance  to  the  student  we  are  ready  to  proceed  with 
our  instructions. 

In  the  lessons  which  follow  the  reader  is  presumed  to 
employ  a  wide  apertured  one-fifth,  one-sixth  or  one- 
tenth  immersion.  We  shall  try,  as  far  as  possible,  to 
make  them  applicable  to  the  use  of  any  good  glass  hav- 
ing air  angle  up  to  175°.  The  higher  balsam  angles 
will,  however,  when  attainable,  be  the  better  instrument, 
with  which,  too,  the  instructions  will  be  the  better  un- 
derstood. The  student  is  also  reminded  that  with  the 


262  HOW   TO   SEE   WITH  THE    MICROSCOPE. 

particular  objective  he  may  employ  he  may  be  in  some 
measure  defeated  in  his  efforts;  still  we  have  to  hope 
that  his  endeavors  will  not  result  in  time  "  totally 
lost." 

Lesson  First. — Place  the  mount  of  Monmouth  rhom- 
boids on  the  stand,  select  the  two-inch  ocular,  mak- 
ing immersion  contact  with  water  or  glycerine,  as  has 
previously  been  directed.  Place  the  collar  of  the  ad- 
justment in  the  middle  of  its  run ;  use  the  light  from 
the  smallest  kerosene  hand  lamp,  placing  the  same  about 
seven  inches  to  the  left  of  the  stage,  the  flame  to  be  on 
a  level  with  the  same,  edgewise  to  the  mirror,  and  two 
inches  in  advance  of  the  front  edge  thereof.  Removing 
all  sub-stage  appliances,  swing  the  radial  bar  so  that  the 
mirror  shall  give  illumination,  say  from  70°  axis;  ma- 
nipulate so  fts  to  light  up  the  field,  using  about  one-half 
the  sized  flame  your  lamp  will  allow.  Now  focus,  and 
having  taken  a  general  look  at  the  "  tout  ensemble," 
select  a  frustule  somewhat  below  a  medium  one  in  size, 
and  bring  to  the  centre  of  the  field,  the  valve  in  a  hor- 
izontal position.  Now  focus  again  carefully,  adjusting 
the  mirror  so  as  to  get  the  very  best  view  attainable. 
Now  study  for  a  moment  the  general  character  of  the 
image.  Notice  particularly  if  there  be  any  distortion, 
or  whether  the  two  ends  are  more  or  less  indistinct  or 
obscured.  Slide  the  object  carrier  and  hunt  up  several 
other  shells  and  examine  individually,  that  ;you  may  be 
assured  that  you  have  a  fair  specimen  to  deal  with. 
Next,  notice  the  edges  of  the  valve ;  compare  the  upper 
with  the  under;  note  if  these  are  tolerably  clean  and 


POSITION    OF    OBSERVER.  263 

sharp,  or  whether  they  are  more  or  less  woolley.  Com- 
pare the  median  line  with  the  upper  and  lower  edges. 
Manipulate  the  fine  adjustment  and  notice  as  to  any 
change  of  focus  necessary  as  between  the  edges  and  the 
median  line;  study  this  median  line  well,  and  you  will 
probably  detect  a  shadow  from  it  shading,  but  only  per- 
haps slightly,  the  lower  entire  half  of  the  shell.  Grasp 
the  mirror  firmly  and  change  its  position  (not  the  radial 
arm)  a  little  in  every  direction,  meanwhile  studying  the 
effect  of  the  shadow  on  the  lower  half  of  the  frustule. 
Hunt  up  other  frustules  and  study  them  in  like  man- 
ner, changing  the  focus  from  time  to  time  as  may  be 
necessary. 

Selecting  an  average  shell,  and  placing  the  same  in 
the  centre  of  the  field,  and  focus  sharply.  Having  ar- 
ranged the  mirror  to  the  best  advantage,  grasp  the  collar 
of  the  objective  with  the  fingers  of  the  right  hand 
(which  now  leaves  the  mirror  just  as  it  was),  those  of 
the  left  hand  being  in  contact  with  the  fine  adjustment, 
withdraw  the  eye  for  an  instant  and  turn  the  collar  of 
the  adjustment  briskly  nearly  a  full  half  revolution; 
placing  again  the  eye  in  position,  focus  quickly  and 
sharply.  Now  undertake  to  decide  instantly  as  to  the 
effects  produced.  Is  there  more  or  less  distortion  at 
the  ends  of  the  shell  than  before?  How  are  the  edges? 
Cleaner  and  sharper,  or  the  reverse?  How  is  that 
shadow  below  the  median  line?  Does  it  shade  the  en- 
tire half  of  the  valve  more  than  was  the  case  formerly, 
or  has  it  consolidated  itself  to  a  narrow  band  under  the 
median  line?  If  you  find  the  least  trouble  in  assuring 


264  HOW   TO    SEE   WITH   THE    MICROSCOPE. 

yourself  instantly,  repeat  the  program  me  until  you  can. 
Now,  reader,  one-half  hour  conscientiously  spent  at  this 
exercise  will  assist  you  more  than  a  half  year  of  pro- 
miscuous practice.  Let  me  advise  you  to  hang-  well  to 
it.  You  must  learn  to  judge  instantly  as  to  the  appear- 
ances to  which  your  attention  has  been  called,  nor  can 
the  least  "  guess-work"  be  allowed. 

Well,  now,  premising  that  you  have  had  sufficient  of 
this  practice,  so  that  you  are  able  to  assert,  without  fear 
of  contradiction,  that  after  the  turn  of  the  collar  adjust- 
ment, there  was,  as  we  will  assume,  evidently  more  dis- 
tortion noticeable  at  the  ends  of  the  valve,  nor  were 
the  edges  as  sharply  defined,  (it  may  be  that  one  edge 
cannot  now  be  seen  without  specially  focussing  therefor.) 
The  shadow,  too,  under  the  median  line  is  not  only  en- 
tirely over  the  entire  lower  half  of  the  shell,  but  it  has 
become  deeper  and  more  offensive  than  before.  The 
fact,  then,  becomes  apparent  that  you  turned  the  collar 
in  the  wrong  direction.  Therefore,  place  the  adjust- 
ment in  its  original  position ;  look  your  shell  well  over, 
thus  to  fortify  yourself.  It  will  be  well,  now,  to  repeat 
the  experiment,  selecting  various  valves  of  the  rhom- 
boides,  and,  having  become  accustomed  to  the  change 
in  appearances,  then  you  may  try  many  of  the  other 
diatoms  to  be  found  on  the  mount.  No  matter  what 
particular  one  may  be  selected,  you  will  in  due  time  be 
able  to  note  the  characteristic  effect  of  this  change  in 
the  adjustment. 

Lesson  Second. — Having  replaced  the  collar  adjust- 
ment to  its  first  position,  and  selecting  a  tolerably  small 


POSITION     OF    OBSERVER.  265 

shell  of  the  rhomboides,  place  it  in  the  centre  of  the 
field,  the  focus  well  adjusted,  etc.  Devote  a  few  mo- 
ments to  a  general  consideration  of  the  nature  of  the 
changes  wrought  by  the  turn  of  the  collar.  Endeavor 
to  gather  up,  as  it  were,  the  experience  gained  by  les- 
son first.  This  done,  removing  the  eye  for  a  moment, 
turn  the  adjustment  in  an  opposite  direction  to  that  of 
lesson  first,  but  not  so  far  in  extent,  and  immediately 
looking  through  the  tube,  adjust  again  the  focus,  and  if 
necessary  adjust  also  the  mirror  until  the  best  view  of 
the  shell  shall  be  obtained. 

Now  if  the  preceding  lesson  has  been  well  studied,  the 
learner  ought  to  recognize  a  decided  improvement,  and 
there  ought,  withal,  to  be  more  general  brilliancy  to  the 
image.  The  shell  should,  so  to  speak,  lay  flatter  in  the 
field.  In  short,  things  ought  to  assume  an  encouraging 
.appearance.  Repeat  the  experiment  several  times,  but 
with  greater  or  lesser  changes  of  the  collar  adjustment, 
until  you  arrive  at  a  particular  point  in  the  adjustment 
which  seems  to  be  about  the  thing.  Having  thus  deter- 
mined this  point,  the  student  may  now,  by  way  of  en- 
couragement, shift  the  position  of  the  object  carrier 
and  bring  one  of  the  larger  shells  to  the  centre  of  the 
field,  when,  with  a  slight  alteration  of  the  mirror,  he 
will  probably  be  rewarded  with  a  fair  view  of  the  trans- 
verse strife.  Assuming  this  to  be  so,  let  the  student 
examine  progressively  other  and  smaller  frustules,  and 
selecting  one  of  the  very  smallest  that  he  can  see,  bring 
it  to  the  centre  of  the  field. 

Lesson  Third.— Replace  the  collar  to  the  initial  po- 


266  HOW   TO    SEE    WITH   THE   MICROSCOPE. 

sition,  as  per  lesson  second,  focus  your  new  shell  and1 
examine  it  critically,  as  has  already  been  directed ;  next* 
repeat  the  turn  of  the  collar,  in  the  same  direction,  but 
varying  the  extent  of  the  movement,  focussing'  again 
as  before.  Bye-and-bye,  when  the  collar  shall  have  been 
turned  to  approximately  the  correct  place,  the  striae  will 
of  course  be  again  visible,  and  it  is  more  than  probable 
will  be  even  better  seen  than  before.  If  this  shall  be 
the  case,  try,  by  slight  manipulations  of  the  mirror 
alone,  to  obtain  the  very  best  display  of  the  lines.  And 
we  now  approach  close  work.  If  the  eyes  are  tired,  or 
the  general  condition  of  health  be  below  par,  it  will  be 
better,  if  any  further  work  be  determined  upon,  to  go 
back  and  take  a  review  of  what  has  already  been  accom- 
plished ;  but  on  the  other  hand,  if  conditions  are  gen- 
erally favorable,  proceed  thus  : 

Lesson  Fourth. — With  your  frustule  as  nicely  exhi- 
bited as  possible,  the  shell  selected  being  as  small  as  you 
can  successfully  attack  to  show  well  the  striae,  examine 
it  well  closely;  see  if  the  upper  and  under  edge  are 
both  equally  well  in  focus.  It  may  be  that  one  edge  is- 
much  better  defined  than  the  other,  or  it  may  be  that 
one  edge  cannot  be  seen  at  all.  This  indicates  that  the 
valve  lies  side  wise  in  the  balsam,  in  which  event  discard 
the  shell  and  hunt  up  another  that  lies  exactly  flat,  and 
of  the  same  size. 

Now  work  over  this  diatom,  generally  as  you  have 
been  instructed  in  the  foregoing  lessons,  accepting  the 
position  you  now  have  of  the  adjustment  as  the  base  of 
farther  trials.  Change  the  collar  to  the  right  or  left. 


POSITION    OF   OBSERVER.  267 

noticing  all  the  points  to  which  your  attention  has  been 
called ;  but  these  various  changes  of  the  collar  should 
be  much  less  limited  in  extent.  We  have  now  further 
items  for  you  to  observe.  Examine  the  strice  carefully; 
see  if  they  continue  quite  to  the  edge  of  the  shell,  or  do- 
they  stop  a  little  short  thereof,  the  edge  becoming  as 
clear,  sharp  and  distinct  as  that  of  a  razor.  Look  with 
an  eagle  eye,  too,  into  that  shadow  under  the  median 
line.  Has  it  become  almost  self-luminous  and  trans- 
parent? And  has  it  drawn  itself  upwards  and  together, 
forming  a  narrow  but  brilliant  band  (so  to  speak)  ad- 
jacent to  the  under  side  of  the  median  line?  Have  all 
appearances  of  diffraction  lines  left?  Does  the  shell  lay 
well  down  and  flat?  All  of  these  interrogatories  must 
receive  your  devoted  attention. 

When  things  are  just  right,  the  valve  laying  flat  iiu 
the  balsam,  the  striae  will  not  quite  extend  to  the  edge 
of  the  shell.  The  dark  band  under  the  median  line 
will  be  contracted  as  described,  but  in  the  place  of  the 
former  dark  and  muggy  shadow,  it  will  have  become 
lively  and  brilliant.  Ditto,  as  to  all  the  other  shadows- 
seen  in  the  field.  In  fact,  everything  has  improved,  be- 
it  a  diatom  or  a  patch  of  dirt.  The  edge  of  your  shell 
ought  to  be  sharply  distinguishable,  not  by  a  line  of 
varying  thickness,  for  there  is  no  line  there,  and  there- 
fore you  ought  not  to  see  anything  of  the  kind.  If  the 
adjustment  be  a  trifle  out,  it  will  sometimes  occur  that 
the  valve  will  seem  to  "rise  up;"  i.  e.,  appear  nearer 
to  the  eye  than  it  should.  It  is  impossible  to  describe- 
on  paper  just  what  I  mean  by  this.  I  have  no  trouble, 


268  HOW  TO   SEE   WITH  THE   MICROSCOPE. 

however,  in  getting-  pupils  to  appreciate  this  phenome- 
non. This  effect  is  the  more  palpable  under  a  high  oc- 
ular, say  the  one-fourth  inch.  Let  the  student  try  the 
highest  one  he  has,  and  he  will  notice  that  a  slight  change 
of  the  collar  will  cause  the  shell  to  "  lay  down  "  prop- 
erly. But  he  must  nevertheless  be  able  to  make  this 
correction  from  noticing  the  condition  when  employing 
the  two-inch  eye-piece.  And  here  it  may  be  observed 
that  with  different  objectives  some  leeway  must  be 
allowed.  It  is  hardly  probable  that  the  student  can 
take  his  particular  object  glass  and  follow  me  to  the 
very  letter;  or  is  it  even  certain  that  the  author  could, 
with  said  glass,  demonstrate  to  an  expert  what  has  been 
written  in  these  instructions ;  yet  after  allowing  due  and 
proper  margin,  the  hints  presented  must  prove  of  value, 
and  if  we  could  have  been  told  as  much  eight  years  ago 
it  would  have  saved  us  hours  and  hours  of  the  toughest 
work.  And  right  here  a  thought  presents  itself,  for- 
eign, perhaps,  to  these  lessons,  but  let  it  go  on  record, 
namely :  If  it  be  so  that  we  can  assist  the  student,  we 
have  in  very  truth  no  mean  reward  for  time  spent  in 
the  past  in  the  study  of  object  glasses. 

Lesson  Fifth. — Having  noted  the  division  correspond- 
ing to  the  exact  adjustment  of  your  objective,  so  that 
you  shall  be  able  to  place  the  collar  at  the  right  spot  at 
once,  without  loss  of  time,  leave  the  rhomboides  and 
examine  your  mount  generally.  Notice  the  play  of  light 
and  shade  over  the  several  diatoms.  Hunt  up  those  por- 
tions of  the  slide  containing  a  mass  of  the  larger  forms 
huddled  together;  in  other  places  you  will  probably 


POSITION     OF    OBSERVER.  269 

find  sediment  congregated  together  in  little  colonies,  the 

O         O  O 

coarser  particles  throwing  an  individual  shadow  over 
the  others.  Observe  these  appearances  closely.  Now 
place  the  collar  intentionally  out  of  adjustment  (prefer- 
ably opening  the  systems),  and  thus  look  over  your 
mount  again.  See,  how  the  shadows  have  become  mixed 
up!  What  a  labyrinth  there  is  to  be  sure!  A  perfect 
plexus  of  indeterminable,  indefinable  shadows  proceed- 
ing from  nowhere  and  ending  nowhere.  The  thickened 
edges  of  the  diatoms  seem  to  cast  a  shadow  on  their 
own  account.  Notice,  too,  how  that  some  of  these 
large  shells  seem  to  have  become  badly  distorted.  Find 
those  little  colonies  again,  and  note  that  the  individual 
particles  thereof  have  lost  their  brilliancy — have  become 
muggy  and  indefinite.  Here,  too,  are  all  sorts  of  shad- 
ows, and  more  or  less  confusion  generally.  Return,, 
now  the  collar  to  its  proper  place  and  review  your 
mount.  Now,  see  how  things  have  improved  in  general 
brilliancy ;  see  how  the  shadows  have  become  harnessed 
properly  into  the  traces.  You  can  trace  them  now,  and 
get  an  idea  of  what  they  mean,  where  they  came  from,, 
and  where  they  end.  Look  at  the  little  colonies  once 
more.  Now  they  are  all  alive  with  brilliancy  and  sparkle 
like  very  diamonds. 

When  the  student  feels  that  he  can  follow  me  thus 
far,  let  him  study  the  tone  of  his  objective.  This  will 
depend  on  the  object-glass  employed.  All  superfine 
objectives  should  be  under  corrected,  i.  e.,  there  should 
be  a  preponderance  of  the  blue;  but  hardly  any  two 
good  objectives  are  exactly  alike,  some  being  under- 


270  HOW  TO   SEE   WITH  THE   MICKOSCOPE. 

corrected  to  a  greater  extent  than  others.*  Whatever 
may  be  the  correction  of  a  given  object-glass,  there 
will  be  a  corresponding  tone  to  the  field,  and  it's  the 
business  of  the  learner  not  only  to  know  the  fact  but 
to  be  competent  to  recognize  the  characteristic  appear- 
ance presented  not  by  the  particular  object  viewed 
alone,  but  by  the  entire  field  of  view.  And  here  again 
•comes  some  nice  eye  work.  The  artist  can  look  at  the 
landscape  and  recognize  the  very  "atmosphere" — not 
so  the  shepherd's  boy.  The  former  might  talk  until 
dooms-day  to  the  latter  as  to  "  atmosphere." 

Now  every  good  object-glass  has  an  "atmosphere" 
of  its  own,  peculiar  to  itself,  and  depending  on  the 
individual  corrections  of  the  glass.  A  moment's  con- 
templation of  the  situation  teaches  the  difficulty  attend- 
ing any  effort  on  the  part  of  the  author  to  make  him- 
self understood  so  as  to  be  of  service  to  the  learner. 
Nevertheless,  the  attempt  shall  be  made. 

Lesson  Sixth. — Place  the  shell  of  rhomboides  exactly 
in-  the  centre  of  the  field,  and  adjust  the  object-glass. 
Arrange  the  mirror  with  its  radial  bar,  so  as  to  illumi- 
nate at  about  45°  or  50°  from  axis.  Focussing  sharply, 
examine  well  your  diatom  as  to  color;  the  chances  are 
that  both  blue  and  red  are  to  be  observed.  Select  in 
turn  several  shells  and  thus  examine,  and  finally  in- 
spect all  the  objects  on  the  mount  before  mentioned. 
A  little  patient  attention  will  teach  you  that  there  is 
something  apparently  clue  to  the  blue  that  does  not 
attach  to  the  red.  For  instance,  the  shells  may  have  a 
slight  lavender  tint ;  as  soon  as  one  can  detect  any- 


POSITION    OF   OBSERVER.  271 

thing  in  this  way  that  is  presumed  to  be  characteristic, 
then  put  the  object-glass  out  of  adjustment  and  focus- 
sing anew  make  the  comparison.  If  the  student  has 
hit  the  proper  effect,  he  will  notice  that  with  the  glass 
out  of  adjustment,  said  effect  has  vanished.  Should  (as 
will  most  probably  be  the  case  with  his  first  efforts)  he 
fail  to  mark  any  characteristic  difference  in  color  or 
tint,  replace  the  collar  adjustment  and  repeat  the  ex- 
periment; selecting,  as  near  as  he  can  judge,  some 
"probability,"  and  again  throwing  the  glass  out  of 
proper  adjustment  examine  again.  The  process  must 
be  repeated  time  after  time  until  the  end  shall  be 
gained.  When  by  dint  of  practice  the  learner  begins 
to  feel  that  he  "  sees  the  point"  let  him  in  a  similar 
manner  examine  all  of  the  other  diatoms  on  the  mount 
until  he  shall  have  become  perfectly  familiar  with  the 
tone  of  his  objective. 

Lesson  Seventh. — Having  mastered  tolerably  well  the 
previous  instructions,  let  the  learner  now  turn  his  atten- 
tion to  the  tone  of  his  field.  This  is  a  finer  "point" 
than  that  of  the  preceding  lesson,  and  demands  in  turn 
more  of  the  eye-training.  The  problem  is  in  all 
respects  similar  to  that  concerning  the  tone  of  the 
objective,  differing  in  this  one  element  only.  The 
student  must  now  endeavor  to  recognize  a  particular 
tone  to  the  whole  field  when  the  object  glass  is  in  per- 
fect adjustment.  The  instructions  are  quite  of  the 
character  as  those  of  the  last  lesson,  an  1  need  not  be 
repeated.  The  two  lessons  might  have  been  reduced  to 
•one,  were  it  not  that  a  little  practice  on  the  former 


272  HOAV   TO   SEE   WITH   THE   MICROSCOPE, 

will,  and  for  the  reason  named,  be  advantageous  before 
studying  the  tone  of  the  field.  These  last  two  lessons 
should  not  only  be  well  studied,  but  the  student  ought 
constantly  to  endeavor  to  improve  in  his  recognition  of 
tone.  Once  having  become  tolerably,  I  may  say,  com- 
fortably expert,  its  practice  becomes  a  second  nature 
and  will  be  persisted  in  from  choice,  meanwhile  the 
observer  becoming  daily  more  and  more  proficient. 

This  characteristic  tone  of  the  field  is  more  apparent 
in  objectives  of  the  highest  balsam  angles,  with  the 
super-excellent  object-glasses  of  the  Messrs.  Spencer  or 
Mr.  Tolles,  when  the  glass  is  exactly  in  correction,  the 
tone  of  the  field  becomes  a  peculiar  and  exceedingly 
delicate  shade  of  apple  green,  which  one  soon  learns  to. 
recognize  by  aid  of  the  teacher. 

In  the  studies  we  have  thus  far  presented,  and  which 
ought  to  enlist  the  occasional  attention  of  the  pupil  for 
at  least  a  month  or  six  weeks,  it  is  taken  for  granted 
that  he  will  meanwhile  use  the  instrument  as  he  may 
elect,  and  either  for  pleasure  or  such  profit  as  he  can 
arrive  at  on  his  own  account.  There  will  undoubtedly 
be  other  objects  brought  into  requisition  not  named  in 
our  lists.  Now,  whatever  practice  he  may  have  of  this 
description,  there  are  some  general  conditions  concern- 
ing high-angled  objectives  which  ought  not  to  be  un- 
heeded, for  example,  let  the  learner  discover  as  near  as 
possible  the  point  ot  the  maximum  aperture  of  his 
glass  ;  it  will  be  well,  too,  that  he  pay  attention  as  to 
thickness  of  the  covers  used.  These  two  points  have  a 
direct  bearing  on  the  pupil's  progress  and  must  not  be- 
neglected. 


POSITION    OF   OBSERVER.  273 

Hand  the  expert  a  strange  mount  of  the  Monmouth 
or  Cherryfield  rhomboides.  It  is  possible  for  him  with- 
out looking  at  it,  and  by  the  sense  of  feeling  alone  to 
state  thus:  "  This  slide  cannot  be  used  with  the  one- 
tenth  and  glycerine  contact.  Use  water  and  with  the 
collar  nearly  at  closed.  If  the  one-sixth  be  employed 
use  glycerine,  and  the  objective  will  correct  within 
four  or  five  divisions  from  the  closed  point."  Either 
statement  being  found  on  the  actual  test  or  trial  to  be 
the  fact.  In  truth,  any  such  statement  from  the  expert 
founded  on  his  sense  of  feeling  alone  would  be  worth 
more  than  two  hours  spent  over  the  tube  by  the  novice. 
Hence  the  importance  of  the  learner's  acquiring  the 
same  tact  ("  knack  "  is  the  popular  word),  nor  is  there 
anything  so  very  difficult  in  its  acquisition. 

Lesson  Eighth. — Returning  to  the  slide  of  Monmouth 
Rhomboides,  and  choosing  a  frustule  somewhat  larger 
than  a  medium  one,  place  it  in  the  centre  of  the  field, 
adjusting  the  objective,  and  displaying  the  striae,  em- 
ploying an  obliquity  of  say  70°  from  axis.  Next  rotate 
the  stage  through  an  arc  of  45° ;  if  necessary  centre  the 
object  again.  It  will  now  have  assumed  a  position  in- 
termediate between  the  horizontal  and  the  vertical. 
Attempt,  by  slight  changes  in  the  position  of  the  mirror, 
to  display  simultaneously  both  sets  of  lines.  The  inch 
ocular  may  now  be  substituted  in  place  of  the  two  inch. 
To  do  this  nicely,  getting  both  sets  with  equal  force, 
requires  indeed  some  little  "  knack."  The  collar  ad- 
justment being  already  correct,  the  manipulation  will 
entirely  be  confined  to  the  illumination.  Possibly  it 

18  Microscopy. 


274  HOW   TO    SEE    WITH   THE    MICROSCOPE. 

may  be  well  to  shove  the  lamp  a  little  farther  away  from 
you ;  i.  e.,  a  little  more  in  advance  of  the  front  edge  of 
the  stage,  or  perhaps  raising  or  lowering  the  wick,  thus 
increasing  or  diminishing  the  amount  of  light,  may  be 
of  service.  This  is  all  that  can  be  written,  and  the 
learner  must  simply  make  the  most  of  and  help  himself. 
Rest  assured  that  both  sets  of  lines  are  there,  and 
if  it  be  that  they  are  not  shown,  the  diatom  is  not  to 
blame.  In  case  of  total  failure  the  observer  may  select 
one  of  the  larger  shells,  proceeding  to  the  smaller  one? 
carefully  and  by  degrees.  With  the  illumination  at 
present  employed  he  cannot  expect  thus  to  show  both 
sets  on  frustules  smaller  than  a  medium  one.  After 
having  mastered,  as  well  as  may  be,  the  Monmouth, 
substitute  the  Cherryfield,  readjusting  the  objective,  as 
a  matter  of  course. 

There  now  remain,  for  future  consideration,  on  the 
slides  of  Monmouth  and  the  Cherryfield,  the  smallest 
frustules  of  the  rhomboides.  These  we  will  pass  over 
for  the  present,  and  in  the  next  lesson  proceed  to  attack 
the  Saxonicas,  from  Leipsic,  Germany. 

Lesson  Ninth. — The  student  will  recognize  the  frus- 
tules on  this  slide  by  their  similarity  to  the  two  slides 
preceding.  The  valves  are  on  an  average  smaller  and 
thinner,  and  in  consequence  weaker  objects  to  deal  with ; 
as  the  saying  is,  they  are  more  "  difficult."  Select  one 
of  the  largest  and  most  vigorous  shells ;  bring  to  the 
centre  of  the  field,  and,  employing  the  inch  ocular,  focus, 
the  illumination  being  about  70°  from  axis.  Now  ex- 
amine closely  your  diatom,  and  see  if  you  can  bring 


POSITION    OF   OBSERVEK.  275 

your  past  experience  to  bear.  Without  attempting-  to 
observe  as  to  the  striae,  reckon  up  the  general  appear- 
ances and  form  some  verdict  as  to  whether  the  glass  is 
in  adjustment.  If  you  decide  that  it  is  not,  make  up 
your  mind  to  what  extent.  This  done,  proceed,  if  ne- 
cessary, to  adjust,  following  the  directions  already  given, 
bearing  now  in  mind  that  all  the  phenomena  previously 
described  will  be  much  fainter  and  less  decided  than  was 
the  case  of  the  Cherryfield  or  the  Monmouth. 

Let  the  student  assure  himself  that  the  shell  before 
him  lays  perfectly  flat  in  the  balsam.  If  this  is  not  the 
case,  it  will  be  impossible  to  see  both  the  upper  and 
under  edges  simultaneously.  These  frustules  are  ex- 
tremely thin,  and  when  one  edge  is  the  lower  of  the 
two  in  the  mounting  medium,  it  will  appear  to  vanish 
out  of  sight.  Accepting  that  the  diatom  is  a  favorable 
one  for  study,  the  learner  will  notice  that  the  upper  and 
lower  edges,  as  the  adjustment  approaches  the  proper 
position,  behave  better  than  was  the  case  with  the  Cher- 
ryfield or  the  Monmouth.  This  is  owing,  of  course,  to 
the  diaphanous  character  of  the  Leipsic.  He  will  there- 
fore endeavor  to  render  these  edges  considerably  sharper 
and  cleaner  than  could  possibly  have  been  the  case  when 
working  over  the  former  slides.  Let  the  pupil  observe 
closely  the  behavior  of  the  shadow  under  the  median 
line.  As  has  already  been  remarked,  the  effects  are  quite 
similar,  but  in  a  less  marked  degree.  The  eye  must  be 
educated  to  the  situation.  Notice,  too,  that  as  the  ad- 
justment becomes  more  perfect  this  shadow  contracts, 
assuming  the  form  of  a  narrow  band  immediately  adja- 


276  HOW   TO   SEE    WITH   THE   MICROSCOPE. 

cent  to  the  median  line,  while  the  entire  lower  half  of 
the  shell  is  of  a  lower  tone  than  that  of  the  upper. 

Should  the  tryo  have  got  along-  thus  far  tolerably 
well,  it  is  more  than  probable  that  he  will  have  been 
rewarded  by  at  least  a  glimpse  of  the  transverse  striae. 
He  may  now,  by  minute  changes  of  the  mirror,  and  by 
raising  or  lowering  the  wick  of  the  lamp,  endeavor  to 
show  the  markings  as  strongly  (that's  a  bad  word)  as 
neatly  as  possible.  Having  thus  succeeded,  look  sharply 
and  see  if  the  lines  extend  quite  to  the  edges  of  the 
frustule ;  it  may  be  that  some  of  them  will  be  found  to 
project ;  in  either  case  something  is  wrong.  Look  first 
to  the  illumination,  and,  observing  the  shadow  line 
under  the  median  line,  endeavor  to  contract  and  render 
this  as  narrow  as  possible.  If  this  does  not  prevent  the 
striae  from  showing  to  the  extreme  edges  of  this  valve, 
then  recourse  must  be  had  to  slight  alterations  in  the 
position  of  the  collar  adjustment.  It  may  be  advisable 
to  try  a  stronger  ocular,  say  the  "  D  "  solid,  if  one  is  at 
hand.  If  under  this  the  lines  seem  to  "  rise,"  try  and 
correct  this,  as  before  instructed. 

This  apparent  "rising"  will  perhaps  strike  the  reader 
as  something  novel.  Certain  it  is  that  we  have  never 
seen  anything  of  the  kind  in  print.  The  effect  was, 
however,  noticed  long  ago  by  the  author,  and  it  soon 
became  one  of  his  "  points"  in  the  tuition  of  his  pupils, 
the  latter,  at  the  onset,  seldom  ever  get  his  meaning. 
Nevertheless,  in  a  very  little  time  they  "  see  it  "  plain 
enough.  We  have  not  command  of  a  word  that  will 
precisely  and  accurately  express  what  we  desire.  It 


POSITION    OF    OBSERVER.  277 

may  be  advantageous  to  the  student  if  we  repeat  ejacu- 
lations such  as  are  heard  from  scholars,  thus :  "  I  can't 
make  this  shell  lay  down."  "  I  have  a  tolerably  good 
show,  but  the  valve  is  restless."  "  You  seem  to  anchor 
your  diatoms;  mine  are  all  out  at  sea."  "The  valve 
will  float  in  spite  of  me."  "I  have  it;  the  shell  lays 
as  quiet  as  a  summer  morn."  "This  valve  seems  to 
come  right  up  to  the  eye-piece,"  (referring  generally  to 
the  one-half  or  one-fourth  inch.)  Such  and  similar  ex- 
pressions we  have  heard  over  and  over  again.  The 
student  can  select  the  one  that  will  be  of  the  most 
service. 

The  tone  of  the  objective  should  be  studied  with  the 
Leipsig,  just  as  has  before  been  noticed  when  discussing 
the  Monmouth  and  the  Cherryfield.  The  observer  may, 
at  the  commencement,  entertain  the  notion  that  in  re- 
gard to  tone,  the  objective  behaves  very  differently  when 
over  the  more  difficult  mount.  If,  however,  the  pre- 
ceding lessons  have  become  perfectly  familiar  there  will 
be  but  little  trouble  in  recognizing  the  same  peculiar 
and  characteristic  tone  not  only  pervading  the  valve, 
but  the  entire  field  of  the  instrument. 

Suppose,  now,  that  the  manipulator,  having  followed 
the  author  with  satisfactory  success  through  the  Mon- 
mouth and  the  Cherryfield,  should  fail  thus  to  do  when 
the  Leipsig  is  taken  in  hand,  thus:  There  appears  a  cer- 
tain indistinctness  accompanying  the  images  of  the  latter, 
besides,  the  valves  seeui  considerably  distorted,  and  the 
band  of  light  behaves  badly;  so  much  so  that  the  direc- 
tions cannot  be  followed  with  any  degree  of  certainty, 


278  HOW  TO   SEE   WITH  THE   MICROSCOPE. 

and  that  several  trials  have  been  ineffectually  made ;  all 
of  which  lead  to  the  same  result.  In  this  case  the  prob- 
abilities are  that  the  objective  is  at  fault,  and  that  any 
attempt  to  work  it  by  anyone,  however  expert,  will 
only  result  in  a  waste  of  time.  .  The  student  ought  not 
to  decide  definitely  until  by  practice  he  shall  be  entirely 
competent  to  judge  for  himself.  We  mention  the  fact 
here,  because  we  know  full  well  that  some  who  may 
read  these  pages  will  try  and  follow  the  author,  employ- 
ing such  objectives  as  they  may  have  at  hand.  Now  it 
might  occur  that  an  object  glass  capable  of  showing  a 
medium  Cherryfield  or  a  Monmouth  very  well  indeed, 
even  cutting  the  larger  shells  into  checks  or  squares, 
responding,  too,  to  all  the  conditions  we  have  presented, 
and  yet  entirely  fail  when  worked  over  any  but  an  ex- 
ceptionally large  shell  of  the  Leipsig. 

It  may  be  apropos  hereto  discuss  another  point  which 
is  suggested  as  we  write:  It  will  be  noticed  that  all 
along-  in  the  course  of  these  lessons  we  have  made  it  obli<r- 

O  f) 

atory  that  the  simplest  illumination  shall  alone  be  em- 
ployed, reserving  for  the  present  any  allusion  to  special 
methods  used  in  the  resolutions  of  the  severest  tests. 
Our  reasons  are  patent.  '  First,  the  little  lamp  recom- 
mended is  in  ordinary  use,  and  is  always  at  hand  when 
wanted;  as  to  its  size,  the  small  lamp  is  even  superior 
to  a  larger  one,  while  the  smaller  model  has  the  advan- 
tage of  burning  less  oil,  is  handier  to  manipulate,  and 
is  the  more  portable  of  the  two.  In  a  former  part  of 
the  book  we  have  acknowledged  the  superior  force  due 
to  modified  sunlight;  nevertheless,  the  latter  is  unfit 


POSITION     OF    OBSZRVER.  279 

for  the  everyday  work  of  the  microscopist.  The  ob- 
server who  depends  thereon  leans  on  a  treacherous  staff. 
Could  we  command  sunlight,  this  objection  would  cer- 
tainly have  less  force;  but  even  in  that  case  we  would 
be  compelled  to  fall  back  on  artificial  illumination  in 
the  evening,  and  eight-tenths  of  all  microscope  work  is 
done  after  sundown.  Hence  it  is  of  profound  import- 
ance that  the  microscopist  select  such  illumination  as  he 
can  at  all  times  control,  and  to  learn  to  make  the  best 
possible  use  of  it.  Again,  all  that  we  have  said  as  to 
sunlight  applies  with  equal  force  to  objectives  that  re- 
quire to  be  worked  with  its  aid.  Let  the  reader  note 
well  this  fact.  It  has  been  our  purpose  here,  as  it  is 
every  day  with  our  pupils,  to  teach  the  use  of  the  sim- 
plest methods,  both  as  regards  illumination  and  other 
items  of  management. 

Returning,  now,  to  our  diatom  slides  again,  we  remark 
that  the  objective  failing,  with  the  stipulated  illumina- 
tion of  showing  the  Leipsig,  might  be  forced  to  do  so 
tolerably  well  by  the  assistance  of  monochromatic  sun- 
light. Admitting  this,  we  still  assert  that  such  a  glass 
is  unfit  for  the  purposes  of  the  working  microscopist 
beyond  those  it  will  respond  to  under  the  conditions 
which  we  have  presented.  It  further  obtains  that  the 
reader  who,  with  such  a  glass,  has  followed  us  through 
the  Cherryfield  and  the  Monmouth,  can  proceed  no  far- 
ther until  we  are  ready  to  change  the  illumination. 
Presuming,  then,  that  the  objective  is  quite  competent, 
and  that  the  observer  has  thus  far  followed  us  in  a  sat- 
isfactory manner,  we  attempt  some  further  hints  and 
suggestions, 


280  HOW   TO    SEE    WITH   THE    MICROSCOPE. 

Lesson  Tenth. — Having  succeeded  in  displaying  the 
striae  of  the  Leipsig,  selecting  one  of  the  larger  and 
most  vigorous  valves,  it  will  be  instructive  to  notice 
once  more,  and  particularly  the  edges  of  the  shell,  it 
the  frustule  is  Hat  and  the  objective  equal  to  the  work. 
There  ought  not,  as  has  been  before  intimated,  be  the 
slightest  indication  of  any  line  bounding  the  shell,  such 
as  would  be  seen  in  a  drawing  on  paper;  but  in  place 
thereof  (so  to  speak),  on  looking  closely,  there  may  be 
discovered,  when  things  are  just  right,  an  exceedingly 
fine  band  of  peculiar  light,  the  exact  tint  of  which  will 
vary  with  the  particular  objective  employed;  and,  as  a 
rule,  the  most  brilliant  tone  will  be  noticed  on  the  upper 
half  of  the  shell.  If  necessary,  manipulate  the  mirror  a 
bit,  and  endeavor  to  "gather  up"  this  baud  so  as  to 
restrict  it  to  the  narrow  space  bounded  by  the  very 
edges  and  the  termination  of  the  striae.  This  band  or 
tint  cannot  be  well  seen  on  the  Cherryfield  or  the  Mon- 
mouth,  unless,  indeed,  on  the  very  smallest  shells,  which 
for  the  present  have  been  held  in  reserve.  Should  there 
be  any  tendency  of  the  "  lines"  to  "rise  up,"  try  a 
deeper  eye-piece,  and,  shifting  the  adjustment  a  trifle, 
seek  to  remove  the  trouble,  returning  to  the  inch  ocular 
as  quickly  as  practicable. 

This  pale  boundary  tint  may,  with  different  glasses, 
assume  quite  different  tints.  With  one  it  may  appear 
as  a  pale  blue;  another  will  show  it  of  a  delicate  fawn 
color,  or  even  a  pale  pink.  Objectives  having  the  most 
perfect  corrections  (I  do  not  mean  the  most  achromatic) 
will  give  this  band  in  what  I  call  an  "  apple  green," 


POSITION    OF    OBSERVER.  281 

and  the  tone  of  the  field  will  be  the  same  as  that  of  the 
band.  The  student  should  practice  until  he  shall  be 
competent  to  recognize  the  band  and  its  accompanying 
tint  according  to  the  particular  glass  employed.  This 
done,  let  him  throw  the  glass  a  little  out  of  adjustment, 
and  it  will  be  seen  that  the  band  has  disappeared,  and 
with  it  so  has  all  the  nice  definition  pertaining  to  the 
edge  of  the  diatom.  Readjust  the  glass  and  watch  for 
its  return  as  you  manipulate.  There  will  be  no  time 
wasted  at  this. 

A  remark  of  a  general  nature  is  in  place  here.  In 
working  over  shells  as  coarse  as  the  Cherryfield  or  the 
rhomboides,  if  the  glass  be  well  adjusted  for  one  valve 
it  may  be  accepted  that  it  is  sufficiently  so  for  all  on  the 
mount.  This  is  neither  strictly  nor  practically  true. 
As  some  of  the  diatoms  lie  nearer  the  cover  than  others, 
the  adjustment  requires  to  be  changed  in  accordance 
with  the  thickness  of  the  intervening  strata  of  balsam ; 
and  on  fine  work,  like  the  medium  frustules  of  the 
Leipsig,  this  point  must  be  kept  well  in  mind. 

Now,  with  this  point  in  mind,  let  the  student,  return- 
ing to  the  Leipsig,  adjusting  his  glass  over  the  same 
shell  we  have  had  in  mind,  getting  things  just  right  "  to 
a  dot,"  let  him  slide  the  object  carrier  and  hunt  up  an- 
other and  similar  valve;  that  is  to  say,  one  that  lays 
just  as  flat  in  the  balsam,  and  of  the  same  size.  Now 
focus,  and  endeavor  to  say  positively  whether  the  new 
shell  is  the  same  depth  in  the  balsam  as  was  the  former. 
If  it  shall  be  the  same  depth,  that  edge  band  will  be 
seen;  otherwise  not.  Practice  this  wett,  hunting  from 


282  HOW   TO    SEE   WITH   THE    MICROSCOPE. 

time  to  time  all  the  larger  frustules  to  be  found  on  the 
mount. 

Before  proceeding  farther-  we  have  to  say  that  the 
foregoing  ten  lessons  must  be  well  studied  and  thor- 
oughly understood.  They  have  been  arranged  and  pre- 
sented so  as  to  lead  the  student  safely  and  progressively 
through  what  has  proved  to  many  a  labyrinth.  We 
have  hinted  at  the  difficulties  which  beset  us  and  satu- 
rate (so  to  speak)  any  attempt  of  ours  to  render  our  in- 
structions perfectly  intelligible  to  all.  It  follows,  then, 
perforce,  that  defects  and  shortcomings  in  the  way  of 
elucidation  ought  to  be  compensated  for  on  the  part  of 
the  pupil  by  his  vigorous  determination  to  master  the 
situation.  Again,  in  the  exercise  thus  far  given  the  in- 
tention has  been  steadily  held  in  mind ;  first,  to  present 
as  plain  a  chart  for  the  guidance  of  the  learner  as  wa$ 
within  our  power;  and,  secondly,  to  keep  well  in  hand 
the  necessary  education  of  his  eyes;  and  in  the  latter 
acquisition  the  element  of  time  is  quite  as  much  a  factor 
as  that  of  diligence  and  determination.  We  strongly 
advise,  then,  the  learner  to  confine  himself  to  the  sug- 
gestions already  given,  until  he  shall  feel  himself  thor- 
oughly and  practically  familiar  with  them. 

Lesson  .Eleventh. — We  will  now  study  the  Monmouth 
or  the  Cherryfield  (either  will  answer  our  purpose)  once 
more.  Place  the  same  on  the  stage,  illuminate  at  an 
angle  of,  say  seventy  degrees  from  axis.  Bring  one  of 
the  largest  shells  to  the  centre  of  the  field ;  adjust  the 
glass  and  focus,  getting  the  very  nicest  display  of  the 
transverse  striae  obtainable.  Now  gradually  let  down. 


POSITION   OF    OBSERVER.  283 

on  the  angle  of  the  illumination  little  by  little,  adjust- 
ing the  mirror  so  as  not  to  lose  the  show  of  the  lines. 
Now  if  the  student  has  studied  well  what  has  thus  far 
been  taught,  he  ought  to  be  astounded  at  two  conditions 
which  will  flash  on  his  intelligence.  In  the  first  place, 
he  will  find  that  he  can  decrease  the  angle  of  the  illumina- 
tion down  to,  say  35°,  all  the  while  holding  the  stria? 
well  in  hand.  The  probability  is  that  he  has  now  too- 
much  light,  and  it  will  be  well  to  try  the  effect  of  turn- 
ing down  the  wick  of  the  little  lamp  a  little.  Having 
tound  the  very  lowest  angle  of  the  illumination  that 
will  command  a  full  show  of  the  striae,  return  the  mir- 
ror just  a  trifle — just  enough  to  reinforce  the  display  of 
the  lines.  Compare  the  effect  with  that  of  the  previous- 
lessons.  Notice  that  your  strise  shell  and  all  have  be- 
come more  transparent.  There  is  not  even  a  suspicion 
of  oblique  illumination.  Your  diatom  (and  all  the 
others  decently  in  focus  in  the  field)  swim  in  a  sea  of 
fire.  That's  a  cold  word — "lightning"  expresses  the 
idea  better.  Observe  how  flat  the  shell  is!  Not  one- 
particle  of  distortion.  Observe,  too,  that  shadow  we- 
have  before  called  attention  to,  under  the  median  line. 
See  how  transparent  it  has  become.  Did  you  say  that 
you  cannot  see  it  at  all?  Yes,  it's  there ;  look  sharp 
for  it  I  Now  look  down  between  the  striae.  See  how 
nicely,  how  exquisitely  they  are  cut  apart.  The  spaces 
between  them  are  as  visible  as  the  striae  themselves. 
Notice,  too,  how  that  the  most  infinitesimal  flickering^ 
of  the  lamp  flame  plays  with  consummate  grace  in  and 
among  the  lines.  Look  well  to  the  edges  of  the  valve. 


284  HOW  TO   SEE   WITH   THE   MICROSCOPE. 

Watch,  when  the  flame  flickers,  for  that  little  band  of 
Light,  and  when  you  catch  it  remark  the  wondrous  deli- 
cacy of  its  tone.  Note,  too,  how  the  flickering-  of  the 
flame  bathes  the  field  with  minute  differences  in  tone, 
things  are  almost  alive.  Compare  what  you  now  see 
with  anything  that  you  saw  a  month  ago.  Has  not  your 
time  been  well  expended? 

When  the  student  has  arrived  at  a  position  that  will 
enable  him  to  fully  appreciate  what  I  am  now  writing, 
he  is  safe.  No  matter  should  he  have  been  accustomed 
to  the  use  of  low  apertures  from  childhood,  he  can  never 
be  forced  to  return  to  his  first  love,  nor  will  he  have 
trouble  in  following  me  to  the  very  end. 

Should  the  learner  unfortunate^  find  that  in  this  les- 
son he  cannot  see  things  as  described,  and  presuming 
that  the  objective  is  competent  for  the  work,  then  it 
must  occur  that  there  is  either  trouble  with  the  manipu- 
lations, or  his  eye  is  not  sufficiently  trained  for  the  work 
in  hand.  Hence  he  cannot  get  the  mirror  far  enough 
downwards;  i.  e.,  he  is  compelled,  in  order  to  see  the 
lines  at  all,  to  use  light  of  too  much  obliquity.  There 
is  but  one  remedy  (if  he  is  sure  as  to  the  capacity  of  his 
objective,  which  he  ought,  perforce  of  the  preceding 
lesson  to  demonstrate),  to  wit:  Practice  until  the  end 
shall  be  arrived  at. 

This  effect,  due  to  the  lesser  illumination,  has,  as  the 
reader  will  remember,  received  our  attention  on  a  fore- 
going page.  It  may  be  advisable  that  he  review  what 
has  been  said,  and  thus  combine  theory  with  practice. 

Lesson  Twelfth. — We  are  now  to  deal  with  the  more 


POSITION    OF   OBSERVER.  285 

difficult  class  of  objects,  such  as  are  recognized  as  the 
severest  tests.  It  will  be  much  better  for  the  student 
if  he  confine  himself  to  the  instructions  already  given , 
until  he  shall  have  become  perfectly  at  home  with  his. 
objectives  and  mounts  before  paying  attention  to  what 
we  shall  here  have  to  offer.  In  the  remainder  of  the 
lessons  the  education  of  the  eye  will  be  an  indispensable 
condition  to  success,  and  the  instructions  can  only  be 
understood  acceptably  by  those  who  have  paid  rigid 
attention  to  the  preceding-  instructions. 

Arrange  the  stand  with  the  inch  ocular,  lamp  and 
mirror,  just  as  described  in  lesson  first.  Get  out  the 
large  bull's  eye  condenser  and  interpose  the  same  be- 
tween the  lamp  and  mirror,  the  flat  side  towards  the 
lamp,  and  within  a  couple  of  inches  from  its  chimney , 
adjust  the  height  of  the  condenser  so  as  to  throw  the 
light  on  to  the  mirror.  The  beam  from  the  lairm  may 
be  slightly  inclined  upwards,  but  never  downwards.  A 
horizontal  beam  is  not  objectionable.  Now  experiment 
a  little.  Try  and  get  the  lamp  as  closely  to  the  left  of 
the  stage  as  practicable,  leaving  room  to  work  the  con- 
denser. Next,  place  the  slide  of  Cherryfield  or  Mon- 
mouth  on  the  stage.  Now  reflect  for  a  moment.  Where 
is  the  point  of  maximum  aperture  of  your  objective? 
And  how  will  the  cover  of  your  mount  respond  to  it? 
If  its  point  of  maximum  aperture  be  at  nearly  "  closed," 
and  your  cover  ot  such  a  thickness  as  will  allow  the 
glass  to  "correct"  nearly  at  closed  with  glycerine,  then 
you  are  to  use  the  same.  If  so  be,  however,  that  the 
cover  is  thick  enough  thus  to  cause  the  glass  to  correct 


286  HOW   TO    SEE    WITH   THE    MICROSCOPE. 

near  closed  with  water  as  the  intermedium,  then,  of 
course,  use  water;  or  it  may  occur  that  the  cover  is  an 
exceedingly  thin  one — so  thin  that  even  with  the  glyce- 
rine the  correction  would  obtain  at  some  considerable 
distance  from  closed,  in  which  case  select  another  very 
thin  cover  to  supplement  that  on  the  mount.  All  this 
has  been  discussed  before,  but  in  the  preceding  lessons 
one  might  have  got  along  tolerably  well  without  par- 
ticular observance  of  these  conditions,  but  not  so  with 
the  problems  we  are  now  about  to  tackle. 

Having  then  decided  tho  above  point  make  the  im- 
mersion contact,  and  selecting  a  medium  shell  of  the 
rhomboides,  bringing  it  to  the  center  of  the  field  focus. 
Arrange  the  mirror  so  as  to  get  the  strongest  illumina- 
tion; let  the  lamp  burn  with  a  moderate  flame;  if  now 
there  is  obviously  too  much  light,  a  perfect  glare, 
bring  the  lamp  closer  to  you  (keeping  the  flame  edge- 
wise to  the  mirror  constantly)  moving  the  same  in  a 
line  parallel  to  the  left  hand  edge  of  the  stage,  readjust 
the  condenser  and  mirror  thus  lighting  up  the  field 
again.  It  will  be  seen  that  the  farther  the  lamp  shall 
be  thus  moved  the  less  will  be  the  illumination.  The 
point  to  stop  at  is  when  you  have  shut  out  the  super- 
fluous sheen  or  glare.  All  this  time  \ve  have  supposed 
that  the  flat  face  of  the  condenser  was  parallel  to  the 
face  of  the  mirror.  Now  change  the  position  of  the 
condenser  causing  it  to  assume  a  slightly  diagonal  pose, 
the  nearer  edge  to  be  swung  away  from  the  stage; 
when  the  condenser  is  exactly  right  the  mirror  will 
have  the  appearance  of  being  traversed  by  a  line  ot 


PORTION     OF   OBSERVER.  287 

light,  that  is,  it  will  not  appear  to  be  equally  illumi- 
nated as  was  the  case  before.  Now  look  to  the  adjust- 
ment of  the  objective,  and  by  slight  manipulations  of 
the  mirror  display  the  striae,  which  will  be  right 
straight  along  work.  Seize  the  base  of  the  condenser, 
stand  firmly,  supporting  the  left  forearm  on  the  edges 
of  the  draw  and  table;  move  the  condenser  just  a  bit 
to  and  from  the  edge  of  the  table,  noticing  the  effect 
in  the  field,  getting  it  thus  in  the  best  position  possible. 
Look  to  your  mirror  again  and  see  if  that  "  line"  is 
still  there;  this  cannot  be  dispensed  with.  Now  if 
the  directions  shall  be  strictly  carried  out,  the  display 
will  be  much  finer  than  possibly  could  have  been  ob- 
tained with  the  former  illumination,  the  diatom  will 
seem  to  swim  in  a  lake  of  fire,  or  as  my  pupils  some- 
times have  said,  "  chain-lightning." 

Do  not  be  satisfied  with  any  apparent  success,  but 
repeat  the  method  of  illumination,  time  and  time 
again,  comparing  notes.  The  student  will  not  prob- 
ably meet  with  perfect  success  the  first  evening, 
although  it  may  be  that  he  will  be  quite  satisfied  with 
his  efforts.  If  it  so  be  that  the  condenser  stands  at 
quite  an  angle,  more  so  than  you  think  ought  to  be  the 
case,  never  mind ;  if  you  have  the  right  effects  in  the 
field,  you  can  study  the  rationale  at  your  leisure.  The 
next  thing  in  order  is  to  study  all  the  appearances 
which  have  been  pointed  out  in  the  preceding  lessons. 

Now  shifting  the  object-carrier,  hunt  up  a  valve  next 
the  very  smallest  on  the  mount,  one  that  lies  flat.  If 
you  are  using  a  one-tenth  your  inch  ocular  will  do,  but 


288  HOW  TO   SEE   WITH  THE   MICROSCOPE. 

if  but  a  sixth,  then  you  will  need  the  "  D"  solid,  the 
one-half  inch.  Try  now  and  display  the  strife  on  the 
little  shell;  remember  that  they  are  at  best  but  very 
thin  and  faint.  Nevertheless,  if  there  has  been  suffi- 
cient practice  with  the  "  lesser  illumination  "  previously 
mentioned,  there  ought  to  be  now  but  little  trouble  in 
recognizing  the  lines.  When  once  a  good  view  has- 
been  obtained,  the  observer  will  be  astonished  by  a 
little  experimenting,  to  find  how  far  the  lamp  wick 
can  be  turned  down — -just  allowing  the  flame  to  peep 
out  of  the  cone — and  still  retain  nice  views  of  the 
strife. 

This  entire  position,  including  that  of  observer, 
stand,  mirror,  and  condenser,  we  have  tried  to  illus- 
trate in  the  cut  on  page  289,  the  diagonal  pose  of  the 
condenser  we  have  intentionally  exaggerated.  It  is 
probable,  too,  that  the  student  may  find  it  necessary  to- 
make  some  slight  changes  to  suit  the  tools  he  may  have 
in  hand.  Let  him  keep  this  fact  prominent,  to  wit,, 
although  the  condenser  will  give  more  light  than  the 
illumination  first  recommended,  nevertheless  there 
must  be  no  more  light  used  than  is  absolutely  required 
to  see  the  object  without  difficulty  as  respects  illumina- 
tion. If  it  be  desirable  at  any  given  time  to  employ  a 
higher  ocular,  always  turn  up  the  wick  of  the  lamp ;  a 
slight  turn  will  be  found  quite  sufficient,  and  while  on 
this  subject  let  me  say  that  nine  out  of  ten  microscop- 
ists  use  far  too  much  light.  They  seem  to  be  impressed 
with  the  idea  that  unless  the  object  is  bedazzled  in  a 
flood  of  light  that  it  is  not  well  shown.  All  this  is  in 


POSITION   OF  OBSERVER, 


19  Microscopy 


POSITION    OF   OBSERVER.  291 

error ;  when  such  illumination  is  employed  the  chances 
are  that  all  fine  detail  of  structure  will  be  drowned 
out,  while  the  effect  on  the  eyes  is  most  injurious.  Keep 
then  the  field  just  as  cool  as  shall  be  consistent  with 
vivacity  and  life,  show  your  objects  brilliantly,  and  see 
that  even  the  shadows  are  lively  and  transparent. 
Grasp  the  mirror  firmly;  get  in  the  habit  of  this; 
when  you  touch  it  at  all  take  hold  of  it  boldly.  There 
is  considerable  for  the  student  to  learn  in  the  proper 
handling  of  the  mirror,  so  as  to  combi  ne  boldness  with 
delicacy  and  efficiency.  Now  as  you  change  its  posi- 
tion just  a  trifle,  notice  the  action  of  the  light.  Does 
it  slide  by  as  it  were,  without  taking  hold?  Or  is  there 
one  particular  position  in  which  the  light  seems  to 
catch  and  "  nip,"  bringing  out  the  makings  with  a  vim. 
Now  if  the  former  is  the  case,  there  is  something  wrong 
(the  objective  being  in  adjustment)  and  perchance  the 
whole  system  of  illumination  will  require  attention  in 
detail. 

When  the  smallest  shell  of  the  Monmouth  and 
the  Cherryfield  have  been  thus  mastered  (as  to  their 
transverse  striae)  those  of  the  Leipsig  may  be  taken  in 
hand,  and  subsequently  the  smallest  valves  of  the  Isle 
of  Shoals;  these  are  quite  as  severe  tests  as  an  ordi- 
nary balsamed  amphipleura  pellucida.  The  slide  of 
Leipsig  ought  to  be  thoroughly  mastered  previous  to 
attacking  the  Isle  of  Shoals;  all  the  peculiar  appear- 
ances which  we  have  from  time  to  time  set  forth,  are 
to  be  studied,  and  as  the  eyes  become  educated  the 
amount  of  obliquity  of  the  illumination  is  to  be  de- 


292  HOW   TO    SEE    WITH   THE   MICROSCOPE. 

creased.  This  Utter  item  is  to  be  a  constant  study ; 
bear  in  mind  this  one  broad  rule,  that  to  use  a  wide- 
angled  glass  well  is  to  work  with  the  least  obliquity 
possible,  and  when  over  easy  tests,  with  more  central 
illumination  that  can  be  effectively  obtained  with  nar- 
row apertured  objectives.  In  short  the  employment  of 
the  wide  apertures  points  to  the  use  of  centrally  dis- 
posed light ;  this  may  be  a  novel  doctrine  to  many,  but 
not  at  all  new  to  the  author. 

Strive  then  to  work  with  the  most  central  illumina- 
tion possible ;  get  rid  of  all  shadows  not  indispensable ; 
as  a  rule  where  the  markings  are  dependent  on  thick- 
ness of  structure,  the  greater  this  difference  of  thick- 
ness, i.  e.,  the  more  prominent  the  markings,  the  less 
will  be  the  obliquity  required;  conversely  the  thinner 
and  the  fainter  the  markings  the  more  obliquity  is 
called  for.  Now  the  smallest  shells  of  the  Isle  of 
Shoals  are  extremely  thin,  the  striae  are  not  so  very  fine, 
probably  not  measuring  closer  than  85  in  .001  English 
inch,  but  they  are  so  thin  and  so  fine  as  to  beat  out  any 
object-glasses,  excepting  those  of  the  higher  apertures. 
And  even  with  these  the  mirror  will  have  to  stand  (ar- 
tificial illumination  being  used  as  directed)  at  least  60° 
to  65°  from  axis ;  a  fine  one-tenth  ought  to  show  any 
and  all  of  them,  either  with  the  one  inch  or  one-fourth 
inch  ocular.  A  similar  one-sixth  will  require  the  half- 
inch. 

Now,  in  the  study  of  the  last  four  or  five  lessons,  the 
student  is  to  constantly  endeavor  to  improve  himself  in 
the  adjustment  of  his  objective.  The  broad  land-marks 


POSITION   OF   OBSERVER.  293 

have  been  laid  down  for  his  guidance,  and  these  should 
not  be  lost  sight  of.  As  his  eyes  become  trained  to  this 
kind  of  work,  he  will  begin  to  pick  up  items  of  value 
on  his  own  account.  Especially  will  he  arrive  nearer  a 
due  appreciation  of  what  we  mean  by  tone  of  objective 
and  field.  He  will  thus  be  able  to  recognize  for  him- 
self, confidently,  too,  when  things  are  just  right.  Ditto, 
when  they  are  not  just  right.  Should  the  collar  of  his 
objective  need  to  be  changed,  he  must  be  able  to  make 
such  change  at  once,  and  in  the  right  direction.  There 
must  be  no  indecision — no  guess  work.  He  will  have 
learned,  also,  that  when  the  adjustment  is  exactly  cor- 
rect, not  only  has  the  display  of  the  striae  become  more 
satisfactory,  but  that  the  general  appearances  of  the 
entire  shells  have  improved.  This  effort  at  improve- 
ment of  the  adjustment  of  the  objective  should  become 
a  constant  and  never  ending  study ;  in  truth,  after  one 
becomes  tolerably  advanced  therein,  it  is  no  longer  a 
"  study,"  but  rather  a  pastime. 

We  desire  to  insist  with  all  the  vigor  we  can  com- 
mand, that  there  is  force  attached  to  the  reciprocal  re- 
lations above  named,  to  wit:  That  when  the  student, 
perforce  of  intelligent  practice,  shall  be  in  position  to 
assert,  dogmatically,  that  his  manipulations  are  correct, 
he  will,  conversely,  be  just  as  competent  to  reaffirm  the 
fact  when  things  are  not  in  proper  adjustment.  When 
this  obtains  to  an  acceptable  extent,  he  will  be  compe- 
tent to  use  his  glass  for  any  field  of  investigation  that 
he  may  elect,  and,  as  a  matter  of  course,  he  will  regard 
those  whom  he  is  assured  have  not  given  proper  atteu- 


294  HOW   TO   SEE   WITH   THE   MICROSCOPE. 

tion  to  this  essential  item,  knowing,  too,  that  it  is  es- 
sential— "cumgrano  salts."  With  our  private  pupils 
we  have  often  tried  amusing-  experiments,  simply  to 
become  assured  of  their  proficiency  in  this  matter,  thus : 
We  sometimes  place  a  drop  of  mucilage  on  the  interior 
surface  of  the  field  lens  of  the  eye-piece,  replacing  the 
same  and  watch  for  results.  If  the  pupil  is  well  trained 
there  is  no  deceiving  him.  He  will  assert  roundly  that 
something  is  the  matter.  If  I  say  to  him,  mildly,  "  why, 
that's  pretty  well,  isn't  it?"  He  replies  at  once,  in  tones 
that  there  is  no  dodging,  "  No,  sir;  there  is  something 
wrong,  sure."  And  then,  again,  I  have  had  the  pupil 
pay  me  back  in  my  own  coin — placing  a  similar  drop  of 
mucilage  in  the  interior  surface  of  my  own  oculars. 

We  have  already  said  that  no  two  lenses  work  ex- 
actly alike.  It  remains,  therefore,  for  the  pupil  to  moke 
a  specialty  of  his  own  object  glasses,  first  assuring  him- 
self, preferably  by  the  advice  ot  some  expert  friend,  that 
he  shall  not  waste  time  over  an  inferior  glass.  While 
he  thus  becomes  more  and  more  familiar  with  his  own 
objectives,  he  will  also  acquire  a  general  knowledge  of 
all,  and  will  in  due  time  be  able  to  take  a  strange  object 
glass  and  work  it  nearly  or  quite  up  to  its  maximum. 

Unless  the  observer  be  provided  with  a  really  super- 
fine objective,  he  can  hardly  make  much  headway  in 
the  examination  of  the  smaller  shells  of  the  Saxonica 
from  the  Isle  of  Shoals.  Should  he  have  much  trouble 
in  getting  the  striae  on  the  very  largest  frustules,  these 
appearing  quite  obscure  and  of  a  generally  uninviting 
aspect,  the  edges  badly  defined,  and  more  or  less  distor- 


POSITION   OF   OBSERVER.  295 

tion  prevailing,  he  may  be  pretty  sure  that  his  glass  is 
at  fault.  His  time  will  therefore  be  much  better  spent 
in  the  examination  of  such  objects  as  come  within  its 
powers.  This  point  is  well  worth  close  attention,  thus, 
perhaps,  saving  a  double  outlay  of  time  and  patience; 
and  there  has  been  a  vast  amount  of  valuable  time 
wasted  in  fruitless  attempts  to  resolve  severe  tests, 
for  which  purpose  the  objective  was  totally  unfit  and 
incapable. 

The  illumination  we  have  just  described  is  quite  suffi- 
cient for  the  display  of  the  transverse  striae  of  either 
slide  of  Amphipleura.  As  we  have  before  stated,  the 
" Bridge  of  Allan"  is  the  easier  of  the  two  and  should 
be  studied  first,  and  the  student  should  give  preference 
to  the  cleanest  shells  on  the  mount.  If  the  smaller 
scales  of  the  Isle  of  Shoals  are  well  seen,  and  the 
"  Bridge  of  Allan  "  resist,  the  fault  will  certainly  be  in 
the  adjustment  of  the  objective  over  the  latter  mount; 
possibly  it  may  occur  that  the  observer  has  selected  an 
exceptionally  difficult  shell  of  the  Pellucida.  The  bet- 
ter way  will  be  to  look  over  the  slide  in  detail,  of  course, 
as  before  advised,  giving  preference  to  the  cleaner  and 
most  inviting  frustule. 

If  so  be  that  the  student  has  the  Moller  probbe  plate, 
the  illumination  given  is  also  quite  sufficient  to  display 
the  Nos.  18,  19,  and  20.  After  he  shall  have  become 
well  advanced,  there  are  some  particular  advantages 
connected  with  the  study  of  this  plate.  He  ought  to 
see  the  Nos.  18  and  19  with  but  little  trouble,  and  in  a 
little  time  with  the  radial  arm  at  45°  from  axis.  On  this 


\ 
206  HOW   TO   SEE   WITH   THE   MICROSCOPE. 

plate  passing  from  No.  19  to  20  is  quite  a  jump.  One 
may  see  the  No.  19  in  a  very  satisfactory  manner,  and 
yet  fail  of  the  No.  20.  At  the  onset  it  will  be  better 
to  secure  all  the  obliquity  of  light  possible.  Should 
the  Acme  or  the  little  Histological  stand  be  used,  the 
upper  one-third  of  the  mirror  may  rise  above  the  stage, 
the  lamp  and  condenser  to  be  adjusted  with  the  greatest 
nicety.  If  the  No.  20  resist  the  attack,  it  is  preferable 
not  to  spend  much  time  over  it,  but  go  at  once  back  to 
the  No.  19  and  endeavor,  by  some  careful  re-adjustment, 
to  get  a  still  better  view  of  this ;  and  when  satisfied  that 
such  has  been  accomplished  then  return  to  the  attack 
on  the  No.  20.  One  will  always  succeed  much  faster  by 
trying  to  improve  what  is  seen  than  by  blindly  working 
over  an  object  of  which  the  desired  details  cannot  be 
displayed  at  all.  The  ease  with  which  the  learner  can 
run  from  one  test  to  another  renders  the  Moller  plate 
very  acceptable  to  the  learner.  Should  it  occur  that 
the  No.  20  make  a  protracted  resistance,  let  the  above 
programme  be  adhered  to,  spending  nearly  all  of  the 
time  in  perfecting  the  display  of  the  No.  19.  It  may 
be  worth  while  to  add  that  the  Moller  Amphipleuras  are 
about  on  a  par,  in  point  of  difficulty,  with  those  from 
Aberdeen,  Scotland.  If  tiiere  be  any  difference,  my 
impression  is  that  of  the  two  the  Moller  No.  20  are 
perhaps  the  easier  test. 

In  studying  the  Aberdeen,  or  in  fact  any  mount  con- 
taining severe  tests,  it  is  always  advisable  to  correct  the 
glass  approximately  by  selecting  some  fine  object,  of 
which  the  details  can  be  displayed  by  such  approximate 


POSITION    OF    OBSERVER.  297 

adjustment.  For  instance,  on  the  "Aberdeen "  it  is 
probable  that  ome  specimens  of  Nitzschia  may  be  found, 
by  hunting  for  them,  and  this  should  be  done  at  once, 
and  the  glass  corrected  as  nearly  as  possible.  An  ap- 
proximate adjustment  will  suffice  to  reveal  the  trans- 
verse striae,  and  the  initial  display  ultimately  improved 
by  force  of  a  little  well  directed  manipulation.  It 
may  occur,  too,  that  some  of  the  nitzschia  are  more 
difficult  than  others.  This  being  the  case,  the  stu- 
dent is  to  master  these  successively  before  attacking 
the  amphipleuras. 

In  the  practice  of  all  the  preceding  lessons,  and  over 
the  test  slides,  it  will  be  essential  that  the  pupil,  after 
having  adjusted  his  glass  as  perfectly  as  may  be,  note 
the  exact  division  of  the  collar  graduations.  This  he 
should  make  a  memorandum  of,  so  that  he  can  be  able, 
if  necessary,  to  readjust  the  objective  to  the  mount 
without  loss  of  time.  But  this  is  not  all.  He  will 
find  that  as  he  acquires  proficiency  by  practice,. that  he 
will,  time  after  time,  change  these  recorded  numbers, 
and  will  be  inclined,  perhaps,  to  smile  at  the  wildness 
attending  his  initial  attempts ;  and  by  thus  comparing 
the  present  with  the  past,  he  may  be  encouraged  as  to 
the  future.  This  habit  of  noting  in  black  and  white 
the  best  attained  adjustment  of  the  objective  from  day 
to  day  should  be  rigidly  persisted  in  for  at  least  a 
twelve-month. 


298  HOW   TO   SEE   WITH   THE   MICROSCOPE. 


WORK   OVER   DRY  MOUNTS  WITH  HIGH  APERTURES   OBJECT- 
IVES. 

After,  and  not  before,  the  student  has  become  profi- 
cient in  the  preceding  lessons,  it  will  be  advantageous- 
for  him  to  procure  dry  mounts  of  the  acknowledged 
diatom  tests,  and  study  well  their  peculiar  action  under 
the  objective.  At  a  glance  it  will  be  noticed  that  the 
dry  frustules  are  much  more  vigorous  than  those  mounted 
in  balsam.  They  have  more  body,  appear  more  solid,, 
the  image  is  stronger  every  way.  Hence  it  is  that  an 
objective  may  shew  a  dry  mount  tolerably  well,  and  yet 
be  utterly  defeated  by  the  same  valves  when  balsam 
mounted.  Should  the  student  be  well  versed  in  our  pre- 
vious instructions,  he  will  find  little  difficulty  in  dealing 
with  dry  mounts.  As  a  rule,  the  latter  are  to  be  illu- 
minated with  pencils  of  less  obliquity  than  objects 
mounted  in  balsam.  In  the  dry  mount,  too,  we  have 
greater  contrasts  of  light  and  shade.  These  differences 
will  be  at  once  noticed  by  the  intelligent  pupil,  wha 
will  find  little  difficulty  in  adapting  himself  to  the  situ- 
ation. He  should  keep  in  remembrance  this  one  fact,, 
to  wit:  That,  owing  to  the  superior  brilliancy  pertain- 
ing to  the  dry  mount,  little  differences  in  the  collar  ad- 
justment are  not  so  perceptible  as  is  the  case  with  bal- 
samed  objects ;  nevertheless,  the  difference  is  there,  and 
well  worth  the  study  necessary  to  recognize  these  little 
differences.  Again,  should  the  learner  desire  to  com- 
pare one  objective  with  another  as  to  their  comparative 


WORK   OVER   DRY   MOUNTS,    ETC.  299 

defining  powers,  always  choose  a  balsam  mount,  and  the 
thinner  and  weaker  the  shells  (within  reasonable  limits) 
the  better  and  the  more  palpable  will  be  the  comparisons. 

We  advise  every  lover  of  a  good  objective  to  provide 
himself  with  a  slide  of  the  genuine  English  podura,  as 
a  matter  of  course  dry  mounted,  and  let  him  be  careful 
to  keep  it  dry!  Amount  that  has  once,  only,  been 
swamped  in  water  will  be  probably  badly  damaged ;  and 
should  it  occur  that  water  leaks  through  the  cement,  it 
should  be  immediately  dried  by  moderate  artificial  heat, 
and  subsequently  laid  away  in  a  warm  place  for  several 
hours.  Too  much  care  cannot  be  taken  with  a  really 
valuable  slide  of  podura.  Prof.  Phin  says,  in  his  excel- 
lent work,  "  How  to  Use  the  Microscope,"  alluding  to 
the  podura  scale,  "  page  after  page  has  been  written  for 
the  purpose  of  showing  how  the  podura  ought  to  look* 
and  still  the  question  seems  to  be  undecided." 

A  year  or  two  ago  a  lively  discussion  sprang  up  in  the 
London  Monthly  Journal  of  Microscopy ,  between  Messrs. 
Piggott  and  Wenham,  the  former  contending  that  the 
true  resolution  of  the  podura  resulted  in  dots.  Mr. 
Wenham,  on  the  contrary,  warmly  taking  sides  with 
Ross  and  Beck,  holding  that  the  "  exclamation  points" 
were  the  proper  thing  to  be  shown.  A  month  or  two 
later  a  most  curious  article  appeared  in  the  *'  Popular 
Science  Monthly"  contributed  by  Mr.  John  Michells,  and 
entitled  "  The  Microscope  and  its  ^/^interpretations." 
The  point  of  Mr.  Michell's  article  was  to  show  the  want 
of  reliability  attending  observations  made  with  the  mi- 
croscope. To  make  this  point  salient,  he  referred  to  the 


300  HOW   TO    SEE    WITH   THE   MICROSCOPE. 

London  controversy  of  the  Messrs.  Piggott  and  Wen- 
ham  on  the  podura  question,  and  also  gave  the  state- 
ments of  other  English  observers.  Among  the  illustra- 
tions accompanying  this  article  were  five  or  six  cute 
showing  the  same  scale  of  Podura  as  seen  in  the  micro- 
scope under  different  illuminations.  Thus  one  identical 
scale  was  exhibited  to  the  reader  as  widely  changed  in 
its  aspects  as  could  have  occurred  had  dissimilar  scales 
been  selected  for  the  comparison.  One  or  two  of  the 
results  shown  were  evidently  owing  to  distortion  occur- 
ring from  the  use  of  a  badly  corrected  objective. 

Now  let  it  be  remembered  that  Mr,  Michells,  in  thus 
stating  his  authority  for  the  misinterpretations  of  the 
microscope,  worked  with  legitimate  material,  and  the 
work  over  the  podura  presented  was  such  as  had  been 
arrived  at  by  English  microscopists  of  acknowledged 
competency.  There  must  be  something  wrong ;  in  what 
direction  shall  we  look  for  the  cause  thereof? 

So  far  as  the  exhibition  of  "  the  markings  "  of  the 
podura  are  concerned,  they  are  an  easy  test ;  i.  e.,  almost 
any  common-place  glass  will  show  them  after  a  fashion, 
while  what  would  be  known  as  a  "  real  honest  working 
sixth  or  eighth  "  will  show  these  markings  with  consid- 
erable force;  and  such  a  display  would  likely  be  as 
acceptable  to  the  novice  (or  to  those  who  had  never 
worked  with  better  objectives),  as  the  view  given  by  a 
superb  high  balsam  angled  glass  by  Spencer  or  Tolles. 
But  mark  this:  Hardly  two  of  the  "  real  honest  work- 
ing glasses,"  owing  to  the  hap-hazard  character  of  their 
corrections,  will  give  the  same  appearances,  while  the 


WORK   OVER    DRY   MOUNTS,    ETC.  301 

objectives  of  Spencer  and  Tolles  will  have  but  one  and 
the  same  constant  story  to  tell.  With  these,  properly 
manipulated,  it  is  impossible  to  get  aught  over  the  po- 
dura  but  the  exclamation  points.  With  these  superb 
glasses  such  a  thing  as  the  reproduction  of  the  several 
appearances  shown  by  one  and  the  same  scale,  as  ex- 
hibited in  the  cuts  by  Mr.  Michells,  becomes  an  impos- 
sibility. And  here,  in  the  opinion  of  the  author,  may 
be  found  the  key  of  the  problem,  to  wit:  The  better 
glasses  showed  the  podura  tolerably  well.  The  poorer 
ones,  those  "  real  honest  working  glasses,*'  of  which  we 
have  heard  so  much  about,  were  bound  to  set  forth  their 
individual  ^^representations,  and  thus  furnish  material 
for  contributions  to  periodical  literature  like  that  of  Mr. 
Michells. 

As  to  the  true  structure  of  podura,  there  can  be 
little  doubt;  there  has  never  been  but  one  opinion 
among  American  observers  accustomed  to  the  use  of 
the  finest  American  objectives,  and  the  spines  or  ex- 
clamation marks  are  accepted  as  the  true  resolution  of 
these  seales.  By  the  aid  of  electricity,  these  spines 
have  been  detached  from  the  body  of  the  scale;  the 
detached  spine  together  with  the  parent  scale  were 
photographed  and  thus  presented  to  the  readers  of  the 
"Lens." 

We  have  already  had  occasion  to  say  that  Mr.  Geo. 
W.  Morehouse,  of  Wayland,  New  York,  was  the  first 
observer  who  demonstrated  the  capabilities  of  the 
Beck  vertical  illuminator;  when  used  in  conjunction 
with  American  object-glasses  of  high  balsam  angles t 


302  HOW   TO    SEE   WITH   THE   MICROSCOPE. 

Mr.  Morehouse's  results  in  displaying-  objects  by  re^ 
fleeted  light  under  the  higher  powers  of  the  microscope 
were  truly  astounding,  and  his  paper  read  before  the 
Dunkirk  Microscopical  Society  of  Dunkirk,  arrested 
the  attention  of  the  author,  who  immediately  repeated 
Mr.  Morehouse's  observations  with  the  liveliest  satis- 
faction. Mr.  Morehouse  particularly  called  attention 
to  the  unrivalled  views  thus  given  of  the  podura, 
adding  that  they  seemed  to  settle  all  question  as  to  the 
nature  of  these  markings.  Mr.  Morehouse  observed 
also  that  near  the  ends  of  scales  the  spines  were  some- 
times to  be  seen  projecting  beyond  the  scale  itself,  and 
the  author  can  affirm  the  same  from  his  experience. 
As  suggested  by  Mr.  Morehouse  the  vertical  illumina- 
tor, from  the  nature  of  its  action — dealing  entirely 
with  surfaces  only — not  only  deprives  Mr.  Mitchell's 
paper  of  argumentative  force,  but  fairly  turns  his 
weapons  against  him,  pointing  to  the  podura,  indeed, 
as  a  very  proper  object  with  which  to  demonstrate  the 
reliability  of  microscope  observations. 

The  student  will  find  the  study  of  the  podura  a  valu- 
able assistance  in  teaching  him  the  behavior  of  fine 
object-glasses  over  dry  mounts,  and  when  he  shall  by 
dint  of  long  practice  become  sufficiently  expert  to  de- 
tect and  appreciate  the  beauty  of  the  display  as  given 
by  balsam  aperture  objectives  as  contrasted  with  the 
work  of  medium  angled  glasses,  he  will  suffer  no  re- 
grets as  to  the  time  and  patience  this  accomplishment 
may  have  cost  him. 

We  have  insisted  on  the  use  of  the  genuine  English 


WORK   OVER   DRY   MOUNTS,    ETC.  303 

podura,  and  as  we  have  stated,  this  slide  must  necessa- 
rily be  selected  by  some  friend  competent  to  the  task. 
The  American  podura  is  quite  inferior  to  the  English, 
yet  of  the  two  a  slide  of  the  very  best  American 
should  be  accepted  rather  than  a  notably  poor  English 
specimen.  The  former  will  be  much  better  than  none 
at  all,  but  let  it  be  remembered  that  the  English  are 
the  desired  thing.  Now  as  to  the  proper  appearance  of 
these  scales  under  the  objective,  we  must  state  that  it 
is  perfectly  impossible  to  give  any  truthful  representa- 
tion on  paper.  The  following  cut 
taken  from  Prof.  Phin's  book, 
copied  from  the  illustrated  cata- 
logue of  the  late  Richard  Beck, 
may  help  matters  some,  and  shows 
the  podura  with  tolerable  precision, 
when  the  same  is  seen  with  a  dry! 
one-eighth,  say  of  130°  aperture! 
magnified  1,300  diameters,  and  illuminated  with  light 
as  central  as  possible.  Now  let  the  student  take  a  half 
sheet  of  writing  paper  and  roll  this  up  so  as  to  form  a 
tube,  and  examine  the  cut  attentively,  looking  through 
this  tube,  as  is  frequently  done  when  examining  draw- 
ings, etc.  Letting  a  strong  light  fall  from  the  direc- 
tion indicated  by  the  shadowed  sides  of  the  markings, 
we  think  that  most  of  our  readers  will  have  no  diffi- 
culty in  noticing  that  the  "  exclamation  points  "  seem 
to  "  rise  up  "  above  (apparently)  the  general  surface  of 
the  scale.  Our  principal  design  in  calling  attention  to 
this  feature  is  that  he  may  thus  recognize  an  effect  to 


304 


HOW   TO   SEE   WITH   THE   MICROSCOPE. 


which  we  have  had  occasion  to  allude  to  in  previous 
pages,  when  treating  of  certain  diatom  tests.  Now 
this  same  effect  is  easily  seen  in  the  podura  when  under 
the  objective,  and  we  have  never  been  entirely  able  to 
get  rid  of  it,  especially  when  a  glass  of  moderate  angle 
is  employed.  Now  the  reader  knows  from  personal 
experience  iust  as  much  of  this  borrowed  cut  as  does 

the  author.  We  will, 
however,  hazard  the 
assertion  that  the  il- 
lumination shown  was 
about  20°  from  axisr 
the  glass  having  aper- 
ture as  above  stated,, 
of  perhaps  120°  or  130°. 
Let  us  imagine  then 
that  we  thus  have  such 
a  display  under  the  mi- 
croscope; and  again, 
that  we  remove  the 
objective  and  replace 
with  another  of  high 

balsam  angle.  In^the  cut  on  this  page  we  have  endeav- 
ored to  depict  the  changes. 

First  it  will  be  seen  that  with  the  radial  bar  in  pre- 
cisely the  same  position  we  have  the  effect  of  greater 
obliquity;  the  shading  is  more  decided  and  (over  the 
tube)  the  lights  are  more  intense  and  brilliant.  Now 
examine  this  cut  with  the  paper  tube ;  it  will  be  ob- 
served that  the  exclamation  points  do  not  "  rise "  so 


WORK   OVER    DRY   MOUNTS,    ETC.  305 

much  as  was  the  former  case.  They  indeed  appear  in 
good  relief,  but  they  do  not  seem  to  float  clear  from 
the  body  of  the  scale;  these  appearances  are  to  be 
watched  under  the  microscope,  and  the  obliquity  of  the 
illumination  diminished  to  the  least  angle  without 
allowing  the  spines  to  rise.  When  the  adjusting  collar 
and  the  illumination  are  just  in  the  correct  position, 
the  small  end  of  the  «'  wedges"  or  "  exclamation  points 
are  to  be  sharply  defined.  These  scales  may  be  exam- 
ined either  in  a  vertical  or  horizontal  position ;  as  a 
general  thing  the  vertical  will  be  the  preferable  posi- 
tion. Most  mounts  of  podura  will  contain  scores  of 
scales,  while  for  the  most  part  there  will  be  less  than  a 
half-dozen  good  ones.  The  student  should  look  care- 
fully to  this,  and  make  the  best  selection  possible.  Ke- 
ferring  to  the  use  of  the  vertical  illuminator,  Mr. 
Morehouse  called  my  attention  to  a  curious  fact  con- 
nected with  the  study  of  these  scales,  namely,  that  the 
smallest  and  most  uninviting  of  these,  as  shown  by 
transmitted  light,  seemed  under  the  vertical  illumina- 
tor quite  as  strong,  vigorous,  and  satisfactory  as  any. 
We  found  Mr.  Morehouse's  observation  true  as  respect 
to  many  other  insect  scales  we  had  occasion  to  examine. 

The  following,  mounted  dry,  will  form  useful  objects 
and  may  be  advantageously  studied  conjointly  with  the 
podura : 

Scales  of  Lepisma  saccharina — Degeeria — Macrotoma 
major — Petrobius  maritimus — Pontia  brassica — Morpho- 
menelaus — Tinea  vestimenti — Gnat — Hipparchia  Janira 
— Wing  of  Gnat — any  of  the  scales  from  the  lepidop- 

20  Microscopy. 


306  HOW   TO   SEE   WITH   THE   MICROSCOPE. 

tera  will  answer  a  good  purpose,  and  in  the  summer 
time  the  student  will  find  a  plenty  of  these  visitors, 
and  from  such  material  many  excellent  mounts  can  be 
prepared  with  little  loss  of  time  and  at  a  slight  ex- 
pense. We  recommend  that  the  pupil  become  well 
accustomed  to  handling  insect  scales  before  attempting 
the  miscellaneous  examination  of  anything  and  every- 
thing mounted  dry  that  perchance  may  be  directly  at 
hand.  After  considerable  proficiency  has  been  secured, 
the  student  may  test  his  powers  thus :  Let  him  pro- 
vide himself  with  a  dry  mounted  trachea,  say  of  a  bee; 
use  the  lowest  ocular,  select  the  strongest  and  most 
vigorous  part  of  the  object  where  the  coils  are  the 
largest  and  the  strongest,  and  adjust  the  glass  as  nicely 
as  possible  thereon.  This  done,  choose  one  of  the 
longest  continuous  coils  and  see  how  far  this  can  be 
followed  towards  the  smaller  end.  Now  having:  arrived 

O 

at  the  limit,  so  that  the  coils  can  but  just  be  perceived, 
manipulate  the  adjustment;  -now  if  you  succeed  in  get- 
ting very  much  better  definition,  the  proof  is  before 
you  that  you  were  in  error  at  the  commencement. 
Make  a  note  of  the  situation,  and  throwing  the  glass 
intentionally  out  of  adjustment  again,  repeat  the  ex- 
periment until  you  shall  be  enabled  to  certainly  make 
the  initial  correction  with  tolerable  certainty  and  accu- 
racy. This  is  first-class  practice,  and  will  be  of  the 
utmost  value  in  general  work  over  dry  mounts.  The 
trachea,  too,  is  a  real  good  test  object.  The  author  has 
worked  ten  hours  at  a  sitting  endeavoring  to  trace 
these  coils  to  the  very  last  end,  but  has  thus  far  met 
with  defeat. 


WORK   OVER   DRY   MOUNTS,    ETC.  307 

As  to  the  general  examination  of  the  various  dry 
mounts,  or  of  histological  preparations  mounted  in 
glycerine,  nothing  but  the  most  general  directions  can 
be  given.  The  previous  study  of  the  diatoms  will 
become  a  valuable  assistance  to  the  student,  and  this 
study  should  be  still  kept  up  in  the  examination  of  dry 
mounts  especially.  Of  such  objects  as  have  palpable 
size,  and  can  be  seen  with  the  naked  eye,  as  is  the  case 
with  very  many  histological  mountings,  the  pupil  must 
expect  more  or  less  annoyance  from  the  interference  of 
the  varipus  shadows,  from  different  parts  of  the  struc- 
ture, situated  in  different  planes.  If,  in  such  a  mount 
it  be  desired  to  examine  critically  minute  details,  make 
it  a  point  to  select  a  bit  of  the  object  that  has  per- 
chance been  accidentally  removed  from  the  main  body, 
and  when  you  prepare  your  own  mounts  keep  this 
point  in  mind.  A  good  general  rule  with  such  mounts 
is  to  keep  the  illumination  as  nearly  central  as  possible. 
In  the  adjustment  of  the  objective  the  same  plan  is  to 
be  adopted,  selecting  when  available  the  smallest 
isolated  fragment,  with  the  illumination  within  35° 
to  40°  from  axis  (or  less)  the  low  angled  sub-stage 
condenser  will  be  valuable.  It  however  requires  some 
study,  as  we  have  found  by  practical  experience,  to 
work  the  condenser  so  as  to  secure  its  best  effects.  It 
is  a  matter,  also,  that  calls  for  the  outlay  of  time  and 
no  little  patience.  Nevertheless,  the  reward  will  repay 
the  effort. 

Through  the  kindness  of  Mr.  Zentmayer,  who  con- 
structed the  apparatus  we  have  been  experimenting 


308  HOW   TO    SEE   WITH   THE   MICROSCOPE  . 

with  condensers  of  very  small  diameter,  several  of 
these  of  varying  focal  lengths  were  fitted  to  the  same 
mounting.  Either  glass  could  thus  be  used  at  pleasure. 
The  mounting  was  conical  and  the  base  being  also  of 
small  diameter,  say  about  one-fifth  of  an  inch,  our  idea 
was  by  this  arrangement  to  keep  the  angle  of  the  con- 
densing lens  as  low  as  possible,  and  by  the  peculiar 
form  of  its  mounting  to  illuminate  as  little  as  possible 
of  the  object  and  with  an  extremely  acute  cone  of  light 
and  at  the  same  time,  allowing  sufficient  lateral  range 
that  the  instrument  might  be  placed  in  as  oblique  posi- 
tion as  possible.  The  idea  seemed  theoretically  sound, 
and  we  have  spent  much  time  in  the  experiments  hoping 
to  give  our  readers  something  of  value,  but  we  were 
doomed  to  disappointment.  (Not  the  first  experiment 
of  ours  which  has  failed).  The  instrument  is  very 
troublesome  to  use,  requiring  often  some  little  time  to 
coax  the  light  through  the  little  cone,  and  when  once 
obtained,  the  slightest  movement  of  the  mirror  will 

O 

destroy  what  has  been  done.  Nor  when  doing  its  best 
were  the  results  any  better  than  those  obtained  by  the 
Gundlach,  or  Beck  cheap  inch  which  has  already  been 
recommended  for  general  condensing  purposes.  We 
still  believe  that  some  improvement  will  be  made  in  the 
direction  of  our  experiment,  and  hope  that  other  ob- 
servers will  make  similar  efforts  until  further  success 
shall  be  secured. 


OIL    IMMERSION    OBJECT-GLASSES.  309 


OIL    IMMERSION    OBJECT-GLASSES. 

Since  the  introduction  of  the  duplex  objectives 
another  form  of  four-system,  wide  apertnred  glass, 
constructed  by  Carl  Zeiss,  of  Jena,  Denmark,  has  made 
its  appearance  in  this  country. 

With  the  advent  of  these  glasses  came  also  the  an- 
nouncement that  their  balsam  apertures  excelled  those 
of  the  American  duplex.  A  novel  feature  in  the 
mounting  of  the  oil  immersions  was  that  they  were  not 
provided  with  adjustment  collar;  it  being  asserted  that 
the  only  requirements  necessary  to  secure  the  perfect 
action  of  the  object-glass  were  to  use  the  same  with  a 
tube  of  exactly  ten  inches  length,  and  to  employ  cedar 
oil  as  the  immersion  medium. 

It  was  further  stated  that  when  these  simple  require- 
ments were  alone  attended  to,  that  no  further  adjust- 
ment of  the  objective  would  be  required,  and  that  the 
performance  ot  the  object-glass  would  be  found  un- 
equaled. 

As  might  be  supposed,  the  above  claims  on  behalf  of 
the  oil  immersions  were  destined  to  receive  attention 
at  the  hands  of  American  microscopists. 

A  fact  well  known  to  experts  concerning  wide  aper- 
tured  objectives  is  this,  viz:  An  object-glass  exactly 
corrected  to  the  eye  of  A  may  not  be  in  exact  correc- 
tion to  the  eye  of  B  without  suitable  change  of  the 
collar  adjustment. 

During  a  sitting  with  Mr.  Chas.  A.  Spencer  at 
Buffalo  last  fall,  the  above  fact  became  immediately 


310  HOW   TO   SEE   WITH   THE   MICROSCOPE. 

apparent.  Mr.  Spencer's  adjustment  of  his  duplex 
one-tenth  objective  (which  we  were  then  using)  being 
invariably  three  divisions  of  the  collar  graduations 
nearer  "closed  "  than  my  own. 

It  is  obvious  therefore  that  an  "  oil  immersion  "  suit- 
ably corrected  to  the  vision  of  Mr.  Zeiss  when  worked 
with  ten-inch  tube,  might  require  a  special  correction 
when  in  the  hands  of  Mr.  Spencer,  or  myself.  Feeling 
therefore  assured  of  the  error  embodied  in  the  popular 
representations  concerning  the  oil  immersions  of  Mr. 
Zeiss,  the  author  solicited  and  obtained  one  of  Mr. 
Zeiss'  circulars,  which,  being  official,  will,  it  is  believed, 
be  read  with  interest.  With  the  exception  that  a  few 
typographical  errors  have  been  corrected,  the  following 
is  otherwise  a  verbatim  copy. 

NEW    OIL     IMMERSION    OBJECTIVES.        ONE-EIGHTH     INCH. 
ONE-FIFTH    INCH. 

"  This  object-glass  is  adapted  to  an  immersion  fluid, 
which  in  refraction  and  dispersion  is  equal  as  nearly  as 
possible  to  the  crcwn  glass,  a  plan  proposed  by  Mr.  J. 
W.  Stephenson,  of  London,  as  a  devise  for  increasing 
the  aperture  and  for  dispensing  with  correction. 

"  The  lens  constructed  on  this  plan — a  four-fold  sys- 
tem of  pp.  one-eighth  focal  length,  calculated  by  Prof. 
Abbe — shows  an  aperture  of  unusual  amount,  combin- 
ing a  most  perfect  definition  with  a  reasonable  working 
distance.  It  works  equally  well  through  thick,  thin, 
and  thick  covering  glass  without  needing  special  cor- 
rection, owing  to  the  identic  refraction  of  the  immer- 
sion-fluid and  the  covering-glass. 


NEW    OIL    IMMERSION    OBJECTIVES,    ETC.  311 

"The  numerical  aperture  of  the  object-glass  (accord- 
ing to  Prof.  Abbe's  definition,  the  product  of  the  sine 
of  angular  semi  aperture  with  the  refractive  index  of 
the  medium  exposed  in  front)  is  brought  to  the  num- 
ber 1.25  exactly,  which  corresponds  to  a  balsam  angle 
of  113°  and  is  in  the  ratio  of  5:4  greater  than  would 
be  the  maximum  aperture,  180°  in  air,  of  a  dry  lens, 
considered  in  its  numerical  equivalent,  the  resolving 
power  correspondingly  affords  a  visible  increase  com- 
pared with  immersion-lenses  of  the  common  system, 
which  generally  do  not  exceed  1.10  in  the  numerical 
equivalent  of  aperture. 

"As  to  the  immersion-fluid  a  large  number  of  ex- 
periences has  shown  the  oil  of  cedar  wood  (ol.  ligni 
cedri)  to  be  the  most  fitted,  though  it  is  in  a  slight 
degree  still  less  refractive  than  ordinary  crown-glass ; 
other  liquids  of  higher  refraction  exceeding  too  much 
in  dispersive  power.  This  oil  (of  which  a  sample  will 
be  sent  with  the  objective)  may  be  got  anywhere  in 
sufficient  purity. 

"For  controlling  its  qualities  or  those  of  other 
liquids,  which  perhaps  might  appear  convenient,  a 
special  test-bottle  is  forwarded  with  parallel  plane  faces 
and  a  prism  of  crown-glass,  cemented  to  the  stop  of 
this  bottle.  The  vertical  spar  of  a  window  seen 
through  the  prism  and  through  the  oil  beneath,  should 
appear  without  a  sensible  defection  and  should  show 
bodies  only  slightly  colored,  if  the  liquid  has  the  right 
quality. 

"  The  pure  oil,  ligni  cedri,  will  afford  the  best  color 


312  HOW  TO   SEE   WITH   THE   MICROSCOPE. 

correction  for  oblique  light;  for  observation  with  cen- 
tral light  the  image  may  be  obtained  still  more  colorless 
if  a  suitable  quantity  of  a  higher  dispersive  oil  (oil  of 
fennel  seeds  or  anise  oil)  be  mixed  with  that  of  cedar- 
wood.  But  in  this  case  the  refraction  of  the  mixture 
should  be  reduced  to  the  original  refraction  of  the  oil 
of  cedar- wood  by  adding  some  pure  olive  oil ;  the  test- 
bottle  being  always  applied  for  regulating  the  mixture. 

"  A  few  other  oils:  The  oil  of  copaiva-balsam  and 
the  oil  of  sandal-wood  approach  so  close  to  the  oil  of 
cedar-wood  in  refraction  and  dispersion,  that  they  may 
be  used  for  it,  instead  of  it,  if  they  should  be  prefer- 
able in  any  respect,  provided  the  test-bottle  has  stated 
the  right  quality  of  the  sample. 

"  The  use  of  these  oils  will  not  be  injurious  to  prepa- 
rations which  are  hermetically  closed,  as  it  is  likewise 
necessary  for  water-immersion,  although  the  black  var- 
nish on  some  slides  (not  on  all)  will  be  slightly  dis- 
solved by  a  prolonged  exposure  to  the  oil,  its  action 
will  not  be  offensive  within  a  moderate  time ;  and  in 
most  cases  any  contact  of  the  fluid  with  the  edge  of  the 
covering-glass  may  be  avoided,  by  the  oil  not  being 
applied  in  a  greater  quantity  than  is  necessary.  A 
minimum  drop  on  the  covering-glass,  and  such  a  one 
on  the  front  lens  being  quite  sufficient  for  observation ; 
besides  that,  the  varnish  of  the  slides  may  be  perfectly 
secured  against  the  oil  by  a  solution  of  shellac  in 
alcohol. 

"  A  special  advantage  will  result  from  this  mode  of 
immersion  for  the  more  difficult  dominions  of  petro- 


NEW   OIL   IMMERSION    OBJECTIVES,   ETC.  313 

graphic  work;  since  rock-slices  for  inspection  with  the 
microscope  will  become  perfectly  transparent,  using" 
the  oil  without  needing  a  polished  surface  or  a  cover- 
ing-glass cemented  on,  and  may  be  observed  to  a 
greater  depth  than  would  be  accessible  to  the  higher 
powers  of  the  ordinary  system. 

"  In  every  case  the  new  object-glass,  not  considering 
the  greater  optical  capacity  in  bringing  out  difficult 
structures,  will  prove  exceedingly  convenient  for  use, 
from  dispensing  with  any  trouble  in  finding  the  right 
•correction. 

4  *  Of  course  the  full  performance  of  the  increased 
aperture  can  be  effective  only  on  preparations  which 
are  mounted  in  balsam  (or  any  other  medium  exceed- 
ing 1.25  in  the  refractive  index)  or  which,  if  mounted 
dry,  perfectly  adhere  to  the  covering-glass.  On  objects 
separated  by  air  from  the  covering-glass  the  lens  will 
not  work  better  than  any  good  immersion-objective 
with  an  aperture  equivalent  to  an  air-angle  of  180°. 

"  Besides  this,  for  displaying  the  full  performance  in 
oblique  light,  the  illuminating-apparatus  must  yield 
pencils  of  greater  obliquity  than  are  directly  accessible 
to  a  slide  from  air.  The  most  simple  devise  forgetting 
light  on  such  an  obliquity  without  needing  a  special 
apparatus  (immersion  condenser)  is  a  plano-convex 
lens  cemented  to  the  under  surface  of  the  slide  by  a 
minimum  quantity  of  oil.  The  ordinary  mirror  of  the 
microscope  brought  to  a  moderate  distance  from  the 
axis  will  now  yield  pencils  of  any  wanted  obliquity ;  a 
lens  fit  for  this  use  will  be  added  to  the  object-glass. 


314  HOW   TO   SEE   WITH   THE   MICROSCOPE. 

"  If  ordered  for  English  microscopes  the  lens  will  be 
perfectly  corrected  for  a  tube  of  ten  inches  exactly,  and 
no  sensible  deviation  from  this  length  would  be  ad  mis- 
sable  without  a  loss  of  perfect  definition.  However,, 
owing  to  the  slight  defect  of  refractive  power  in  the 
oil  of  cedar-wood,  some  advantage  may  be  found  by 
lengthening  the  tube  for  one-half  to  one  inch  while  ob- 
serving through  extremely  thin  covers  (less  than  0.004 
inch),  and  by  shortening  it  for  one-half  to  one  inch  in 
the  case  of  very  thick  covers  (exceeding  0.008  inch).* 

"  The  object-glass  is  made  with  fixed  brass  work  and 
with  standard  screw  (like  all  my  object-glasses) ;  the 
price  of  it  is  240  marks ;  the  price  of  the  one-twelfth 
is  320  marks ;  the  aperture  guaranteed  to  be  not  less- 
than  it  is  stated  above.  The  lenses  are  screwed  together 
with  moderate  pressure  and  may  be  unscrewed  without 
great  effort,  but  I  caution  expressly  against  unscrew- 
ing them ;  owing  to  the  great  aperture  the  system  is- 
extremely  sensible  to  the  slightest  defect  of  centering 
the  smallest  particle  of  dust,  or  the  least  moisture  get- 
ting into  the  screws,  and  the  unavoidsible  difference  of 
pressure  when  screwing  the  lenses  together,  would 
cause  a  sensible  loss  in  the  performance  of  the  glass."1 

JENA,  March,  1878.  (Signed)        CARL  ZEISS. 

One  can  hardly  read  the  foregoing  somewhat  contra- 
dictory document  without  arriving  at  the  conviction 
that  Mr.  Zeiss  has  suffered  severely  at  the  hand  of  his 
translator.  Be  this  as  it  may  it  will  be  noticed  that  he 
asserts  that  the  oil-immersions  practically  NEED  adjust- 

*  Italics  mine,  J.  E.  S. 


NEW    OIL    IMMERSION    OBJECTIVES,    ETC.  315 

ment,  which  adjustment  he  recommends  be  accom- 
plished by  manipulating  the  draw-tube  to  a  possible 
extent  of  two  inches  when  working  over  covers  varying 
from  0.004  to  0.008;  and  here  let  the  reader  be  re- 
minded that  these  figures  do  not  by  any  means  express 
the  maximum  variations  of  cover-glasses. 

o 

I  have  had  an  opportunity  of  critically  examining  but 
one  of  these  objectives,  a  one-eighth,  imported  by  a 
friend.  This  glass  when  worked  with  ten-inch  tube 
over  my  usual  covering-glasses  required  downright 
engineering  of  the  draw-tube;  furthermore,  when 
worked  over  covers  0.008  inch  thick,  it  was  impossible 
to  correct  the  glass  at  all,  as  the  draw-tube  of  my 
stand  when  fully  closed  would  not  decrease  the  distance 
sufficiently  to  secure  the  proper  correction  of  the  ob- 
jective. 

The  performance  of  this  one-eighth  (when  exactly 
corrected)  was  very  fine  indeed,  and  closely  resembling 
the  work  of  the  Tolles  or  Spencer  duplex.  Superb  as 
its  definition  was,  it  did  not  excel  that  of  my  Spencer 
duplex  one-fourth — a  glass  of  half  its  nominal  power. 
The  balsam  aperture  of  the  one-eighth  was  about  the 
same  as  that  of  my  duplex  glasses. 

During  my  first  evenings  with  the  oil  immersion  the 
cedar  oil  behaved  very  well,  but  on  the  second  and 
third  sittings  it  made  me  trouble  enough.  With  the 
tube  inclined  (as  usual)  the  oil  would  most  unaccount- 
ably take  a  notion  to  run  away ;  when  this  occurred, 
any  attempt  to  reinforce  by  adding  more  of  the  oil, 
made  things  worse ;  the  only  remedy  was  to  clean  the 
slide  nicely  and  commence  operations  again,  de  novo. 


316  HOW  TO    SEE   WITH   THE   MICROSCOPE. 

The  author  learns  from  good  authority  that  Mr. 
Zeiss  has  recently  extended  the  balsam  aperture  of  his 
oil-immersions  improving  thereby  the  performance. 

Oil-immersions  are  now  made  by  Mr.  Tolles  and  Mr. 
Spencer.  These  makers,  however,  supply  the  collar 
adjustment  (as  should  have  been  done  by  Mr.  Zeiss). 
Mr.  Spencer's  objectives  we  are  informed  are  arranged 
so  as  to  work  with  oil  or  glycerine  contact. 

While  in  the  oil  business  as  above  stated,  it  occurred 
to  me  to  try  the  effect  of  various  oils  with  my  duplex 
glasses.  After  a  little  experimenting,  I  found  that 
ordinary  kerosene,  well  washed  in  alcohol,  worked 
most  beautifully  with  both  the  Tolles  one-tenth  and 
the  Spencer  duplex  one-fourth,  with  either  glass  when 
thus  immersed  I  got  the  most  exquisite  displays  of  the 
most  difficult  known  tests.  It  thus  came  to  the  surface 
that  I  had  harbored  oil  immersions  while  ignorant  of 
the  fact. 

That  the  cedar  oil  diminishes  the  range  required  in 
process  of  adjusting  for  varying  thickness  of  cover 
must  be  granted,  hence  the  novice  using  the  Zeiss  im- 
mersions being  necessarily  restricted  to  this  more  lim- 
ited range  might  possibly  get  better  initial  perform- 
ance than  would  result  in  his  first  attempts  to  manipu- 
late a  Tolles  or  Spencer  four-system  objective. 

In  dispensing  with  the  cover  adjustment  and  its 
accompanying  mechanism  (such  as  furnished  by  Spencer 
or  Tolles),  falling  back  on  the  clumsy  draw-tube  as  a 
substitute,  the  cost  of  construction  is  materially  re- 
duced. Those  affected  with  the  res  angusta  dorni  might 


NEW   OIL   IMMERSION    OBJECTIVES,    ETC.  317 

doubtless  contract  with  either  Tolles  or  Spencer  for 
objectives  on  the  model  of  the  Zeiss,  and  fully  equal  to 
the  latter  in  performance,  and  at  figures  considerably 
below  those  quoted  in  the  Danish  catalogue. 

Our  experience  with  the  Zeiss  oil  immersions  has 
neither  weakened  our  appreciation  of  the  screw-collar 
adjustment,  nor  our  high  estimation  of  wide  apertured 
objectives  of  American  manufacture. 


CHAPTER  VIII. 

A  WORD   OR   TWO   ON   VOLUMETRIC   ANALYSIS. 

The  value  of  the  microscope  to  the  medical  profes- 
sion is  greatly  enhanced  by  the  conjoint  use  of  a  little 
chemistry;  in  the  examination  of  urinary  deposits  it 
will  often  occur  that  neither  the  microscopical  nor  the 
chemical  analysis  per  se  would  be  complete  or  entirely 
satisfactory,  while  the  combined  results  of  these  might 
lead  directly  to  the  information  desired. 

Micro-chemical  examinations  of  urines  are  of  the 
utmost  importance  to  the  practitioner;  among  the  best 
English  works  on  the  subject  may  be  named  those  of  Gold- 
ing  Bird,  Beale,  Roberts  and  Harley.  The  beginner  will 
derive  much  satisfaction  from  the  work  of  Dr.  Bird, 
which  although  written  twenty  years  ago  is  essentially 
good  at  this  day.  The  reader  should  keep  in  mind  in 
the  perusal  of  either  of  the  above  authors,  that  micro- 
scopy has  of  late  years  suffered  material  advancement, 
hence  it  is  with  the  superior  objectives  now  at  our  com- 
mand, we  are  able  to  cross-question  some  of  the  plates 
contained  in  the  above-named  books. 

Almost  anyone  looking  over  the  representations  of 
44  tube-casts"  as  pictured  by  Dr.  Beale,  would  natu- 
rally arrive  at  the  conclusion  that  there  could  be  no 
doubt  as  to  the  recognition  of  these  objects  in  practice. 
It  becomes  my  duty  to  say,  therefore,  that  in  neither 
of  the  works  referred  to,  can  be  found  a  reliable  repre- 

318 


ON     VOLUMETRIC   ANALYSIS.  319 

sentation  of  a  genuine  ' « tube-cast " ;  while  on  the  other 
hand  the  learner  depending  entirely  on  the  information 
conveyed  to  the  eye  by  the  plates  is  surely  liable  to  be 
misled.  It  is  very  far  from  our  purpose  to  make  any 
attack  on  the  English  authorities  mentioned;  from 
either  of  them  we  have  derived  a  great  deal  of  useful 
and  valuable  information,  and  they  are  to-day  works, 
to  which  we  make  frequent  reference.  And  then  again 
we  doubt  seriously,  if  an  accurate  idea  of  a  "  pale 
hyaline  cast "  can  be  conveyed  by  means  of  drawings. 
The  learner,  however,  may  rely  on  the  text  of  our 
favorite  authors,  and  at  the  same  time  use  due  care 
that  not  every  adventitious  filament,  hair,  etc.,  be  ac- 
cepted as  a  genuine  "  tube-cast." 

To  detect  with  certainty  a  genuine  "  cast,"  one  of 
the  feebler  order  requires  just  as  much  care  and  study 
as  would  be  required  to  show  the  lines  on  the  Nos.  18 
or  19  of  the  Moller  test  plate,  and  requires  also  just  as 
good  instrumentation. 

Having  thus  alluded  to  one  serious  source  of  error, 
we  have  to  say  that  it  is  no  part  of  our  purpose  here  to 
write  a  treatise  on  urinary  deposits,  although  we  hope 
to  accomplish  something  in  this  line  at  no  distant  day 
our  present  purpose  is  to  give  the  medic  a  hint  or  two 
as  to  the  little  apparatus  required  in  the  volumetric 
analysis  of  urines,  and  to  instruct  him  in  the  prepara- 
tion of  the  necessary  chemical  solutions  employed  in 
such  analysis;  $15.00  or  even  less  will  purchase  a  tol- 
erably effective  outfit. 


320  HOW   TO   SEE   WITH   THE   MICROSCOPE. 


APPARATUS. 

Six  test  tubes ;  let  four  of  these  be  large  size.  Spirit 
lamp.  Four  or  five  two-ounce  beakers.  Bink's  250 
grains  burette.  Two  or  three  small  glass  funnels,  say 
ot  two-ounce  capacity.  Filters  to  match  the  above. 
Two  or  three  glass  rods.  Two  or  three  brushes  for 
cleaning  test  tubes ;  ditto,  for  burette.  Litmus  paper, 
blue  and  red.  Two  measuring  pipettes,  one-half,  one 
and  two  fluid  ounces.  Urinometers. 

All  of  the  above  can  be  obtained  of  Messrs.  GK  Tie- 
man  &  Co.,  67  Chatham  street,  New  York,  and  will 
cost  less  than  $7.00 

Additional  to  this  list  we  recommend  the  purchase  of 
three  or  four  "  Marais  "  graduated  tubes  for  approxi- 
mative analysis.  These  cost  $1.50  each.  At  least  one 
of  these  should  be  provided. 

A  delicate  balance,  one  turning  with  one-fourth  grain 
when  loaded  with  an  ounce  in  each  pan,  will  be  required. 
Most  of  the  books  treating  on  volumetric  analysis  de- 
mand that  the  balance  should  be  quite  an  expensive  one. 
Nevertheless,  the  simple  little  models  which  can  be  pro- 
cured almost  anywhere,  and  costing  less  than  $3.00,  can 
be  made  to  answer  tolerably  well.  Those  to  whom  the 
expense  is  not  objectionable  will  find  a  really  fine  bal- 
ance enclosed  in  a  glass  case  a  luxury.  Ours,  made  by 
Troenmer,  of  Philadelphia,  turning  with,  say  one-fiftieth 
of  a  grain,  costing  $40.00,  has  given  excellent  satisfac- 
tion. Reliable  instruments,  by  Becker,  can  be  obtained 
in  the  cities,  at  prices  from  $10.00  upwards.  Those  who- 


APPARATUS.  321 

have  used  them  speak  highly  of  them;  but  for  the  pur- 
poses of  the  practitioner,  such  instruments  are  not 
strictly  a  necessity.  The  small  German  scales  found  in 
the  office  of  almost  any  physician  can  be  made,  with  a 
little  attention,  to  do  very  fair  work.  If  such  be  se- 
lected, it  will  be  of  the  very  first  importance  to  possess 
a  reliable  set  of  weights ;  those  furnished  with  the  cheap 
instruments  are  not  to  be  tolerated.  Nor  is  it  safe  to 
appeal  to  the  nearest  druggist.  The  safest  method  is 
to  make  one's  own,  which  is  accomplished  with  no  great 
outlay  of  time  or  money. 

First,  purchase  a  set  of  Troemner's  "aluminum" 
grain  weights,  costing  fifty  cents.  These  consist  of  a  five, 
four,  two  three's,  two,  one,  and  one-half  grain  weights. 
With  these  in  hand  it  will  be  easy  to  construct  an  accu- 
rate set.  Specific  directions  are  unnecessary.  . 

A  thousand  grain  bottle  will  also  be  wanted.  This 
can  be  purchased  in  the  shape  of  a  regular  "specific 
gravity  bottle;"  its  cost  is  $2.00.  The  practitioner  can 
readily  adapt  an  ordinary  bottle  to  the  purpose,  simply 
selecting  one  of  such  capacity  that  when  a  volume  of 
one  thousand  grains  of  rainwater  at  60°  F.  is  placed 
therein,  the  water  shall  rise  part  way  in  the  neck,  and 
its  place  marked  with  a  file,  we  have  on  hand  some  halt- 
dozen  1,000  grain  bottles,  which  we  have  picked  up  from 
time  to  time,  and  which  are  in  regular  use,  the  specific 
gravity  bottle  being  held  in  reserve  as  a  standard,  or 
for  the  determination  at  times  of  the  density  of  liquids. 

Imprimis. — Let  me  recommend  to  the  practitioner  that 
he  eschew  the  entire  system  of  weights  as  recognized 

21  Microscopy. 


322  HOW   TO    SEE   WITH    THE    MICROSCOPE. 

by  the  profession,  and  confine  himself  to  that  one  simple 
unit — the  grain.  This,  in  the  case  of  chemicals,  can  be 
adopted  with  perfect  ease,  and  much  confusion  thus 
avoided.  In  the  following  pages  no  other  weight  will 
be  mentioned.  Referring  to  liquid  measures,  the  case 
would  be  somewhat  modified,  and  we  shall  have  occasion 
probably  to  speak  of  fluid  ounces,  drachms,  etc.  Now 
there  are  two  fluid  ounces  in  vogue;  the  one  is  known 
as  the  English  "  imperial,"  and  is  equivalent  to  a  volume 
of  distilled  water  at  60°  F.,  weighing  437.5  grains. 
This,  also,  is  the  ounce  avoirdupois.  The  United  States 
Standard  fluid  ounce  is  quite  another  thing.  This  is  equal 
to  a  volume  of  distilled  water  at  60°  F.,  weighing  455.69 
grains,  sixteen  such  ounces  making  one  pint.  The  United 
States  ounce  will  be  the  one  referred  to  in  this  book, 
when  speaking  of  fluid  ounces  and  drachms,  eight  of  the 
latter  being  equal  to  one  of  the  former.  The  practi- 
tioner should  keep  in  mind  these  differences  between  the 
United  States  and  the  English  fluid  ounce,  when  reading 
English  authors. 

In  the  selection  of  his  chemicals  for  the  preparation 
of  the  standard  solutions,  the  utmost  attention  must  be 
paid  to  their  purity.  They  should  not  be  bought  at  the 
"nearest  drug  store."  It  will  be  always  advisable  to 
purchase  them  from  leading  dealers.  The  formulas 
which  will  be  given  relate  only  to  pure  chemicals.  Due 
attention  also  should  be  given  to  the  manipulations, 
that  the  chemicals  shall  not  become  contaminated.  Even 
after  the  standard  solutions  are  successfully  prepared, 
the  careless  operator  may  ruin  a  solution  by  thought- 


APPARATUS.  323 

lessly  pouring  the  remaining  contents  of  the  burette 
(after  an  analysis)  into  the  wrong  bottle.  The  same 
glass  rod  ought  not  to  be  used  in  different  solutions 
without  being  cleansed.  Every  bottle  should  hive  its 
own  stopper,  and  these  should  not  become  interchanged. 
Every  piece  of  apparatus  used  in  an  analysis  should,  at 
the  termination  thereof,  be  immediately  cleansed. 

The  practitioner  will  find  it  convenient  to  make  his 
several  standard  solutions  in  quantities  of  3,000  grains. 
With  the  exception  of  the  one  used  for  the  determina- 
tion of  sugar,  they  all  have  reliable  keeping  properties, 
and  as  3,000, grains  can  be  made  with  about  as  little 
trouble  as  1,000,  it  is  an  economy  of  time  to  do  so. 

Procure,  if  possible,  suitable  bottles  for  the  standard 
solutions,  furnished  with  a  "  pouring  lip."  These  are 
so  much  handier  in  filling  the  burette.  Ours  were  ob- 
tained from  an  ink  manufactory,  and  answer  the  purpose 
perfectly.- 

Analysis  for  Urea  —  Standard  Solution.  —  Weigh 
thirty-eight  and  six-tenths  grains  of  pure  red  oxide  of 
mercury  and  place  the  same  in  a  large  test  tube,  add  a 
little  nitric  acid,  c.  p.,  and  apply  the  heat  from  the  spirit 
lamp.  The  oxide  will  appear  to  crust  and  little  inclined 
to  dissolve.  By  keeping  up  an  uniform  heat,  mean- 
while stirring  with  a  glass  rod,  the  oxide  will  become 
gradually  dissolved.  Should  it,  however,  become  neces- 
sary, add  a  little  more  acid  carefully,  little  by  little, 
maintaining  the  gentle  heat  and  stirring  with  the  rod 
until  all  of  the  oxide  shall  be  dissolved,  the  object  being 
to  use  the  least  amount  of  acid  possible.  The  process 


324  HOW   TO    SEE    WITH   THE   MICROSCOPE. 

being  completed,  pour  the  whole  into  a  thousand  grain 
bottle,  rinse  two  or  three  times  with  distilled  water, 
adding  this  to  the  measuring  bottle,  and  finally  add  dis- 
tilled water  to  make  the  whole  to  1,000  grains.  Let  it 
stand  for  a  few  hours,  after  which  time  should  there 
form  a  precipitate  of  the  basic  salt,  add  two  or  three 
drops  more  of  the  acid.  The  solution  may  now  be 
transferred  to  the  regular  bottle  for  use.  Two  hun- 
dred grains  of  this  standard  solution  are  (should  be) 
equivalent  to  one  grain  of  urea. 

Baryta  Solution. — In  one  bottle  make  a  cold  solution 
saturated  with  nitrate  of  baryta;  four  ounces  of  dis- 
tilled water  will  be  sufficient.  In  another  bottle  satu- 
rate eight  ounces  of  distilled  water  (cold)  with  caustic 
baryta.  When  the  solutions  are  fully  saturated,  which 
may  be  known  by  the  baryta  remaining  in  excess  in  the 
two  bottles,  allow  a  little  time  for  the  two  solutions  to 
become  clear;  then  carefully  decant  as  much  as  possible 
of  the  nitrate  solution  into  your  regular  bottle,  and  to 
this  add  twice  the  volume  of  the  caustic  solution,  the 
two  combined  forming  the  baryta  solution  for  use  in 
analysis. 

Carbonate  of  Soda  Paper. — In  a  bottle  prepare  a 
saturated  solution  of  carbonate  of  soda.  When  fully 
saturated  pour  into  a  large  dish  or  platter,  provide 
sheets  of  ordinary  printing  paper,  saturate  these  and 
suspend  the  sheets  until  quite  dry;  cut  into  strips  one 
inch  wide  by  six  or  seven  inches  long,  and  preserve  in  a 
wide  mouthed  bottle  fitted  with  a  well-fitting  stopper. 

Measuring  Bottle. — Procure  one  of  the  long  and  slim 


APPARATUS.  325 

four-drachm  bottles  found  at  almost  any  druggist's,  say 
with  an  interior  calibre  of  one-fourth  inch.  Mark  this 
with  a  file  at  heights  corresponding  to  50,  66,  100  and 
200  grains.  This  is  easily  accomplished  with  the  aid  of 
the  burette.  The  plain  bottles  without  a  neck  are  to  be 
preferred. 

The,  Analysis  for  Urea. — Take  a  sufficient  quantity 
of  the  urine,  and  if  albumen  is  present  clear  it  from  the. 
same;  next,  pour  into  the  measuring  bottle  to  the  100 
gram  mark.  Transferring  this  to  a  common  wineglass, 
in  a  like  manner  measure  50  grains  of  the  baryta  solu- 
tion; add  this  to  the  other  in  the  wine-glass,  pour  the 
whole  on  a  dry  filter,  receiving  the  filtrate  in  another 
glass.  Should  the  liquid  come  through  clear,  it  is  well ; 
if  not,  it  must  be  re  filtered  until  it  does.  Three  or  four 
filtrations  at  the  most  will  generally  accomplish  the  de- 
sired end.  While  the  filtering  is  in  operation  fill  the 
burette  to  the  "0"  mark  with  the  standard  solution. 

With  the  measuring  pipette  transfer  one-half  drachm 
of  the  clear  filtrate  to  a  clean  wineglass,  adding  half  its 
quantity  of  distilled  water.  Have  in  readiness  a  strip 
of  the  carbonate  of  soda  paper  and  a  glass  rod.  Deliver 
the  standard  solution  from  the  burette  to  the  filtrate  as 
long  as  any  precipitate  is  distinctly  seen  to  form,  stir 
'with  the  rod,  and  place  a  drop  from  the  glass  in  contact 
with  the  paper,  waiting  a  moment  to  observe  the  reac- 
tion. If  the  paper  continues  white,  add  again  from  the 
burette,  and  stir  again,  placing  a  second  drop  on  the 
paper,  and  thus  continue  carefully  until  the  drop  trans- 
ferred to  the  paper  strikes  a  yellow  color.  Now  look 


326  HOW   TO   SEE   WITH  THE   MICROSCOPE. 

among  the  previous  drops  on  the  paper  and  see  if  there 
are  any  indications  of  the  yellow.  If  so,  you  have  used 
too  much  haste,  and  the  analysis  must  be  repeated.  If  to 
the  contrary  the  yellow  is  only  to  be  observed  at  the  last 
test  made  on  the  paper,  the  analysis  is  ended.  Read  the 
burette,  multiply  this  number  by  12  -r- 100  and  you  will 
have  the  number  of  grains  to  the  fluidounce  of  urine. 

It  will  be  well,  before  making  a  practical  use  of  the 
standard  solution,  to  test  the  same.  Proceed  thus : 

Procure,  say  one-fourth  ounce  of  pure  urea.  This  can 
be  had  of  the  leading  druggists  at  a  cost  of  about  twenty- 
five  cents.  Of  this  weigh  carefully  two  grains,  which 
dissolve  in  200  grains  of  water.  Take  50  grains  of  the 
solution  and  tritate  as  above.  When  the  carb.  of  soda 
paper  strikes  a  yellow  color,  desist  and  read  the  burette. 
Now  the  50  grains  of  solution  contained,  of  course,  one- 
half  grain  of  urea,  and  the  burette  should,  if  the  stand- 
ard solution  have  been  properly  prepared,  read  at  the  100 
mark.  If  the  reading  should  be  less  than  the  100,  the 
solution  is  too  strong,  and  must  be  weakened  by  the  fur- 
ther addition  of  distilled  water.  If,  on  the  contrary, 
the  reading  should  be  more  than  100,  the  solution  is  too 
weak,  and  more  of  the  mercury  must  be  prepared  and 
added.  For  the  purposes  of  the  practitioner  there  is 
no  necessity  of  being  over  precise.  If  the  burette  shows 
but  a  small  error,  plus  or  minus,  it  will  be  sufficient  to 
note  the  fact  on  the  label  of  the  bottle,  applying  a 
proper  correction  to  the  future  analyses.  In  the  exam- 
ination of  the  reactions  on  the  carb.  of  soda  paper,  es- 
pecially in  the  evening,  we  find  a  hand-magnifier  of 
much  service. 


APPARATUS.  327 

Chloride  of  Sodium  —  Standard  Solution. — Dissolve 
forty-four  grains  pure  nitrate  of  silver  in  3,000  grains 
of  distilled  water;  employ  a  clear  white  glass  bottle 
and  set  the  same  in  the  sunlight  for  eight  or  ten  hours. 
A  dark  brown  or  black  precipitate  will  probably  form ; 
when  this  settles  to  the  bottom,  filter  into  a  clean  bot- 
tle, decanting  carefully  so  as  not  to  disturb  the  sedi- 
ment; 200  grains  of  this  standard  solution  should  equal 
one  grain  of  chloride  of  sodium.  Before  being  put  to 
practical  use  the  solution  must  be  tested. 

Solution  of  Ohromate  of  Potash  is  made  by  saturat- 
ing three  or  four  ounces  of  distilled  water;  an  excess 
of  potash  remaining  undissolved  is  not  objectionable. 

To  Test  the  /Standard  /Solution.. —  Procure  a  nice 
clean  lump  of  "  rock  salt,"  crush,  and  select  of  the 
cleanest,  ten  or  fifteen  grains ;  powder  roughly  and  dry 
with  care,  using  but  gentle  heat.  When  thoroughly 
thy,  dissolve  two  grains  in  two  hundred  grains  of  dis- 
tilled water,  and  of  this  measure  fifty  grains  into  a 
wine-glass,  add  a  little  water  and  one  or  two  drops  of 
the  potash  solution.  Fill  the  burette  and  tritate.  The 
addition  of  the  first  drops  of  silver  to  the  salt  solution 
may  be  followed  by  the  appearance  of  a  red  precipi- 
tate, but  on  stirring  with  the  glass  rod  this  will  re- 
dissolve  ;  continue  the  addition  of  the  silver  little  by 
little,  stirring  well  after  each  addition,  until  the  further 
delivery  of  the  silver  is  followed  by  a  permanent  pre- 
cipitate imparting  a  red  color  to  the  contents  of  the 
wine-glass.  This  finishes  the  test,  and  if  the  standard 
solution  is  of  the  proper  strength,  the  burette  will 


328  HOW   TO    SEE   WITH   THE   MICROSCOPE. 

read  at  the  one  hundredth  mark ;  if  too  strong-  or  too 
weak,  add  silver  or  water  as  the  case  may  demand,  and 
repeat  the  test.  The  indications  of  the  burette  furnish 
a  ready  guide  as  to  the  amout  of  correction  necessary, 
hence  the  second  test  ought  to  be  sufficient. 

Analysis  of  Urine  for  Chloride  of  Sodium. — Filter 
say  one-half  ounce  of  the  urine,  and  with  the  measur- 
ing pipette  introduce  one  fluid  drachm  of  the  filtered 
urine  into  a  wine-glass,  and  add  three  volumes  of  dis- 
tilled water,  and  also  two  or  three  dr^ps  of  the  satu- 
rated potash  solution.  Now  with  a  bit  of  litmus  paper 
test  the  reaction  of  the  mixture ;  it  should  be  rendered 
faintly  alkaline  by  adding  Carbonate  of  soda,  or  dilute 
nitric  acid  as  may  be  found  necessary.  Fill  the  burette 
and  tritate  according  to  the  directions  given  above, 
until  the  permanent  precipitate  makes  its  appearance. 
Now  read  the  burette,  divide  this  number  by  twenty- 
five  which  will  give  you  the  number  of  grains  of 
chloride  of  sodium  per  fluid  ounce  of  urine. 

Should  the  specimen  of  urine  be  very  high  colored 
it  may  be  somewhat  difficult  to  detect  the  first  appear- 
ance of  the  permanent  precipitate,  hence  the  accuracy 
of  the  analysis  will  be  impaired.  In  such  cases,  there- 
fore, it  is  better  first  to  decolorize  the  urine;  this  is 
tolerably  well  accomplished  by  adding  a  drop  or  two  of 
a  solution  of  permanganate  of  potash,  and  with  the 
spirit-lamp  bring  the  mixture  nearly  to  the  boiling 
point.  A  brown  precipitate  will  be  observed  which  is 
to  be  removed  by  filtration,  and  the  filtrate  used  for 
the  analysis  according  to  the  preceding  directions. 


APPARATUS.  329 

Analysis  for  Chlorides  Approximately. —  Fill  a 
Marais  graduated  tube  to  the  ounce  mark  with  fil- 
tered urine,  make  strongly  acid  with  nitric  acid;  pro- 
vide z,  solution  ot  nitrate  of  silver,  forty  grains  to  the 
ounce  of  water;  add  an  excess  of  this  to  the  urine  in 
the  tube,  allowing  the  whole  to  remain  quiet  for  twenty- 
four  hours.  At  the  expiration  of  this  interval  the 
volume  of  precipitate  may  be  read  from  the  graduated 
scale,  each  .2c.c.  of  precipitate  will  equal  0.19  grains 
of  chloride  of  sodium ;  in  the  above  approximate  anal- 
ysis the  acid  must  not  be  omitted,  otherwise  a  precipi- 
tate of  phosphate  of  silver  might  vitiate  the  results. 

Analysis  for  Phosphoric  acid. — Dry  carefully  a  suffi- 
cient quantity  of  chemically  pure  nitrate  of  uranium, 
using  gentle  heat;  of  this  take  106 J-  grains  and  add 
3,000  grains  of  distilled  water;  200  grains  of  this 
standard  solution  equals  one  grain  of  phosphoric  acid. 

Solution  of  Acetate  of  Soda. — Four  hundred  grains 
of  acetate  of  soda  are  dissolved  in  six  fluid  ounces  of 
water,  and  to  the  solution  add  800  grains  of  acetic 
acid.  The  commercial  article  known  as  "No.  8"  will 
answer. 

Solution  of  Ferro -cyanide  of  Potassium  is  made  by 
dissolving  one  part  of  the  salt  in  ten  parts  of  wrater. 

Test  Solution. — Dissolve  50.4  grains  of  phosphate  of 
soda  in  1,000  grains  of  water;  100  grains  of  this  solu- 
tion equals  one  grain  of  phosphoric  acid. 

To  Test  the  Standard  Solution. — Measure  fifty  grains 
of  the  above  test  solution  into  a  beaker;  add  one-fourth 
volume  of  the  acetate  of  soda  solution,  increase  the 


330  HOW   TO    SEE    WITH   THE   MICROSCOPE. 

volume  of  this  mixture  three-fold  by  the  addition  of 
water;  fill  the  burette  with  standard  solution,  and 
have  in  readiness  a  white  plate  or  saucer,  on  which 
have  been  placed  several  separate  drops  of  the  ferro- 
cyanide.  Heat  the  contents  of  the  beaker  over  the 
spirit-lamp,  and  keeping  the  same  tolerably  warm,, 
tritate  with  caution,  and  when  a  drop  from  the  beaker 
on  being  placed  in  contact  with  the  ferro-cyanide 
strikes  a  brown  color,  the  analysis  is  ended;  and  if  the 
standard  solution  is  of  the  proper  strength,  the  burette 
will  read  at  the  100  mark.  Any  error  of  standard 
solution  noticed  is  to  be  corrected  and  the  analysis  re- 
peated with  the  standard  solution  as  amended. 

Analysis  of  Urine  for  Phosphoric  acid. —  With 
the  pipette  measure  two  fluid  drachms  of  the  urine 
into  a  beaker,  and  to  this  add  one-half  drachm  of  the 
acetate  of  soda  solution,  also  an  extra  drachm  or  so  of 
water;  have  ready  the  white  plate  and  the  ferro-cyanide 
solution;  warm  the  contents  of  the  beaker  over  the 
spirit-lamp,  and  maintaining  the  heat,  tritate  as  in  the 
above  test;  continue  the  addition  of  the  standard  solu- 
tion until  the  drop  from  the  beaker  when  in  contact 
with  a  drop  of  the  ferro-cyanide  shall  strike  a  brown 
color,  which  terminates  the  analysis.  Read  the  burette,, 
the  number  shown  divided  by  fifty  will  indicate  the 
number  of  grains  of  phosphoric  acid  to  the  fluid  ounce 
of  urine. 

Analysis  with  the  Marais  Approximate  Tubes. — 
The  tube  is  to  be  filled  to  the  ounce  mark  with  filtered 
urine,  add  also  two  drachms  of  the  acetate  of  soda  solu- 


APPAKATUS.  331 

tion,  afterwards  add  an  excess  of  a  solution  of  nitrate 
of  uranium  (one  to  ten) :  placing1  the  thumb  over  the 
end  of  the  tube ;  mix  thoroughly  and  allow  the  tube  to 
remain  quiet  for  twenty-four  hours,  after  which  time 
the  volume  of  precipitate  may  be  read  off,  ever  2cc 
— .016  grains  of  phosphoric  acid. 

Analysis  for  Earthy  Phosphates,  using  the  Marais 
Tubes. — Fill  the  tube  to  the  ounce  mark  with  filtered 
urine  as  above,  add  an  excess  of  strong  liquor  ammonia  j 
mix  well  and  set  aside  for  twenty-four  hours,  at  the 
end  of  this  interval  note  the  volume  of  precipitate; 
each  2cc  will  correspond  to  .06  grains  of  the  earthy 
phosphates. 

Analysis  for  Sulphuric  acid  Standard  Solution. — In 
3,000  grains  of  distilled  water,  dissolve  forty-five  and 
three-fourth  grains  of  pure  chloride  of  barium;  200 
grains  of  this  standard  solution  are  equivalent  to  one 
grain  of  sulphuric  acid.  If  the  solution  be  prepared 
with  due  care,  it  may  be  used  without  special  testing 
as  it  cannot  be  very  well  tritated. 

Solution  of  Sulphate  of  Soda. — One  part  of  soda  to 
ten  of  water. 

Analysis  of  Urine  for  Sulphuric  acid. —  With  a 
pipette  measure  two  fluid  drachms  of  urine  into  a 
beaker,  dilute  this  with  twice  as  much  distilled  water, 
adding  also  two  or  three  drops  of  hydrochloric  acid; 
bring  the  beaker  over  the  spirit-lamp  until  the  contents 
become  hot,  fill  the  burette  with  the  standard  solution ; 
deliver  from  the  burette  into  the  beaker  a  few  drops 
which  will  cause  an  instant  precipitate  of  the  sulphate 


332  HOW   TO   SEE   WITH   THE   MICROSCOPE. 

of  baryta;  this  will  gradually  sink  to  the  bottom  of 
the  beaker;  continue  thus  the  addition  until  no  further 
precipitate  can  be  detected  by  the  eye.  By  waiting  a 
few  moments  the  liquid  above  the  precipitate  will  be- 
come clear,  when  another  drop  or  two  of  the  standard 
solution  may  be  added.  Should  this  cause  a  further 
precipitate,  continue  in  like  manner  to  add  the  standard 
solution;  when  no  further  precipitate  forms,  place  a 
few  drops  of  the  sulphate  of  soda  solution  in  one  of- 
the  smallest  test  tubes,  and  to  this  add  a  drop  or  two 
from  the  beaker;  if  a  white  precipitate  appear  in  the 
test  tube,  the  standard  solution  has  been  added  to  the 
beaker  in  excess ;  and  if  the  precipitate  be  very  dense, 
the  analysis  will  have  to  be  repeated,  using  greater 
care  towards  the  latter  part.  The  number  of  grains 
finally  shown  by  the  burette,  divided  by  fifty,  indicates 
the  number  of  grains  of  sulphuric  acid  to  the  fluid 
ounce  of  urine. 

The  final  determination  in  this  analysis  as  to  the  pre- 
cipitation of  all  the  sulphuric  acid  renders  this  tritation 
somewhat  more  troublesome  to  the  beginner  than  the 
preceding.  The  practitioner  should  therefore,  by  re- 
peated trials,  become  acquainted  with  the  details.  In 
examining  the  test  tube  as  to  the  precipitate,  it  should 
be  held  to  strong  light,  and  a  hand  magnifier  we  have 
found  to  be  of  material  assistance. 

Analysis  for  Sugar — Standard  Solution. — Dissolve 
51 .98  grains  of  pure  sulphate  of  copper  in  500  grains  of 
distilled  water.  Keep  this  in  a  bottle  by  itself. 

Dissolve  caustic  soda  in  distilled  water  until  the  spe- 


APPAKATUS.  333 

cific  gravity  becomes  1.12,  or  the  specific  gravity  may 
be  determined  by  the  use  of  Baume's  hydrometer,  which 
should  float  at  16  J°.  To  each  1,000  grains  of  this  solu- 
tion add  259.90  grains  of  pure  cry stalizedl&ochelle  salts. 
This  constitutes  the  caustic  solution. 

One  volume  of  the  copper  solution  mixed  with  two 
volumes  of  the  caustic  solution  forms  Foldings  Stand- 
ard Solution,  200  grains  of  which  are  equivalent  to  one 
grain  ot  sugar. 

These  solutions  must  be  kept  separate  until  wanted 
for  use,  mixing  only  the  quantity  required  from  time  to 
time.  The  copper  solution  is  quite  stable,  but  the  other 
is  liable  to  deteriorate  by  keeping.  It  will  be  advisable 
for  the  practitioner  to  use  the  caustic  solution  from  an 
ounce  bottle  fitted  with  a  tight  stopper,  which  can  be 
refilled  from  time  to  time,  the  stock  bottle  being  kept 
in  a  cool,  dark  place.  On  mixing  the  two  together  a 
precipitate  forms  which  will  immediately  disappear  on 
shaking.  Should,  on  boiling  the  same,  the  liquid  retain 
a  clear  blue  color,  it  is  in  good  condition.  Heat  should 
always  thus  be  applied  in  advance.  By  complying  with 
the  directions  given,  the  caustic  solution  can  be  kept  in 
order  for  years ;  and  it  is  well  to  make  enough  at  once 
to  last  for  at  least  a  year,  and  the  physician  is  reminded 
that  this  Fehling's  test  for  sugar  is  daily  in  demand. 

Test  of  Standard  Solution  for  Sugar. — Dissolve  four 
grains  of  pure  grape  sugar  in  400  grains  of  water. 
This  solution  should  always  be  used  when  freshly  made. 
In  the  preceding  analysis  it  will  be  observed  that  the 
burette  has  been  filled  with  the  standard  solution.  Now 


334  HOW   TO    SEE   WITH   THE   MICROSCOPE. 

in  the  operation  for  sugar  this  is  not  the  case.  There- 
fore fill  the  burette  to  the  "  0  "  mark  with  the  graduated 
solution  of  grape  sugar.  Into  the  measuring  bottle 
before  described  measure  66  grains  ot  the  copper  solu- 
tion, the  proper  height  being  marked  on  the  bottle  with 
a  file.  Add  of  the  copper  solution  to  that  in  the  meas- 
uring bottle  to  make  the  volume  equal  to  100  grains. 
We  then  have  100  grains  of  the  standard  solution  mixed 
for  use,  and  which  are  equivalent  to  J  grain  of  suo-ar. 
Pour  the  standard  solution  from  the  measuring  bottle 
into  the  largest  test  tube ;  rinse  the  former  with  a  little 
water,  and  add  this  to  that  in  the  test  tube,  bringing 
the  latter  over  the  spirit  lamp ;  heat  to  the  boiling  point, 
and  notice,  first,  if  the  standard  solution  retains  its 
clear  blue  color;  if  so,  proceed  to  tritate,  adding  from 
the  burette  a  few  drops  at  a  time,  bringing  the  mix- 
ture, after  each  addition,  to  the  boiling  point.  Con- 
tinue thus,  adding  from  the  burette  until  the  blue 
color  of  the  mixture  in  the  test  tube  shall  have  almost 
entirely  disappeared.  At  this  stage  of  the  decom- 
position of  the  copper  the  mixture  in  the  tube  will 
have  become  thick  and  of  a  greenish  yellow  color,  and 
will^show  but  little  disposition  to  settle  clear.  Now 
add  cautiously  a  few  drops  from  the  burette;  bring  to 
the  boiling  point  again,  and,  holding  the  tube  in  an  in- 
clined position  near  a  sheet  of  white  paper,  observe  the 
thin  edge  of  the  liquid  as  to  color.  Should  there  appear 
a  trace  of  the  blue  yet,  continue  the  addition  from  the 
burette,  and  also  the  heat,  until  the  last  trace  of  the 
blue  shall  have  disappeared.  Resting  the  tube  in  a  ver- 


APPARATUS.  335 

tical  position,  wait  a  moment  or  two,  and  if  the  reduc- 
tion of  the  copper  be  complete,  the  sediment  will  sink 
in  a  very  short  interval  of  time,  to  the  bottom  of  the 
tube ;  and  if  care  has  been  taken  not  to  overdo  the  thing, 
i.  e.,  introducing  more  than  was  necessary  from  the 
burette,  the  analysis  is  completed  and  the  burette  may 
be  read. 

Now  the  100  grains  of  the  standard  solution  in  the 
test  tube  would  require  j-  grain  of  sugar  for  its  reduc- 
tion, and  50  grains  of  the  solution  in  the  burette  will 
contain  |  grain  of  sugar.  The  burette  should  therefore 
be  lead  at  50°.  The  student  is  advised  to  repeat  the 
operation  several  times  until  he  shall  have  become 
familiar  with  the  reactions.  The  quantity  of  test  solu- 
tion is  ample  for  this.  If,  after  satisfactory  trials,  it 
shall  be  found  that  the  standard  solution  is  to  strong  or 
too  weak,  water  or  copper  may  be  added  to  the  copper 
solution  without  making  any  change  in  that  of  the 
caustic,  and  the  test  should  again  be  repeated. 

Analysis  of  Urine  for  Sugar. — Prepare  the  standard 
solution  for  use  just  as  has  been  directed;  i.  e.9  measur- 
ing 66  grains  of  the  caustic  solution,  and  adding  the 
copper  solution  to  make  the  volume  of  100  grains. 
Pour,  as  before,  into  the  largest  test  tube,  rinsing  the 
measuring  bottle,  adding  the  "  wash  "  to  the  contents 
of  the  tube.  A  very  little  clear  water  may  also  be  added 
to  the  tube.  Fill  the  burette  to  the  "  0  "  mark  with 
the  urine  to  be  analyzed,  bring  the  test  tube  over  the 
spirit  lamp,  and  heat  to  ebulution.  Now  go  on  and 
tritate  just  as  directed  in  the  preceding  test,  observing 


336  HOW   TO    SEE    WITH   THE    MICROSCOPE. 

due  care,  when  near  the  complete  decomposition  of  the 
copper.  When  this  shall  be  obtained,  and  the  blue 
color  of  the  standard  solution  has  disappeared,  the  sedi- 
ment in  the  tube  being  also  inclined  to  settle  quickly, 
the  burette  may  be  read. 

Now,  to  determine  the  amount  of  sugar  from  the 
reading  of  the  burette  is  a  simple  question  of  the  "  rule 
of  three,"  suppose  that  the  number  marked  by  the  bu- 
rette to  have  been  228,  then  it  follows  that  228  grains 
of  the  urine  contained  J  grain  of  sugar;  Hence  456 
(one  ounce)  of  the  urine  would  contain  1  grain  of  sugar, 
or,  as  we  would  say,  "  one  grain  per  ounce."  It  may 
be  well  to  suggest  to  those  who  have  allowed  their 
mathematics  to  become  a  little  rusty,  that  even  in  solv- 
ing proportions,  simple  as  are  the  computations,  that  it 
is  necessary  to  look  after  one's  decimal  points.  Thus, 
in  the  above  example,  the  expression  would  be  —  45(> 
X  0.50, —228  =  unity. 

Use  of  the  standard  solution  in  the  ordinary  testing 
for  sugar.  The  practitioner  will  very  often  have  occa- 
sion to  simply  test  for  the  presence  of  sugar,  when  the 
exact  amount  is  not  necessary.  In  fact,  after  becoming 
thoroughly  familiar  with  the  behavior  of  the  chemicals, 
he  will  be  enabled  to  give  a  close  guess  as  to  quantity. 
The  urine  should  in  all  cases  be  cleared  from  albumen. 
To  merely  detect  the  presence  of  sugar  it  is  only  neces- 
sary to  pour  a  dozen  drops  or  so  of  the  copper  solution 
into  one  of  the  largest  test  tubes  (these  are  always  bet- 
ter when  there  is  boiling  to  be  done),  and  to  add  twice 
the  volume  of  the  caustic  solution.  Bring  to  the  boil- 


APPARATUS.  337 

ing-  point,  and  add  urine  to  the  tube  directly,  continuing 
such  additions  and  bringing'  to  the  boiling  point  sub- 
stantially as  in  performing  the  regular  analysis.  If, 
when  the  amount  of  urine  thus  introduced  shall  be  equal 
to  the  original  volume  of  the  test  solution,  and  there  be 
no  change  of  color,  it  may  safely  be  assumed  that  sugar 
is  not  present. 

Even  when  the  regular  analysis  is  contemplated,  the 
preliminary  trial  test  should  be  instituted.  For  instance, 
we  do  not  care  to  attempt  the  regular  analysis,  when 
by  the  rough  test  we  are  assured  that  there  is  no  sugar 
in  the  specimen.-  Again,  when,  by  the  trial  test,  it  shall 
be  found  that  sugar  is  present,  and  in  large  amount, 
then  it  may  sometimes  be  better  to  dilute  the  urine 
with  an  equal,  or  even  six  times  its  volume  of  water; 
of  course,  allowing  for  this  reduction  in  the  computa- 
tions after  reading  the  burette;  the  accuracy  of  the 
analysis  is  enhanced  by  the  dilution  ot  the  urine.  It 
may  be  further  remarked  that  different  specimens  be- 
have somewhat  differently.  The  directions  given  will, 
however,  be  found  ample,  and  the  practitioner  having 
frequent  use  for  the  sugar  test  in  a  short  time  becomes 
perfectly  at  ease  with  the  manipulations. 

Analysis  for  Albumen. — The  volumetric  method,  one 
of  "trial  and  error,"  involving  several  nitrations,  is 
somewhat  tedious ;  too  much  so  for  the-practical  pur- 
poses of  the  medical  practitioner.  The  author  was 
hence  induced  to  experiment  with  the  "Marais"  ap- 
proximate tubes  comparing  results  with  those  obtained 
by  two  of  the  regular  methods.  These  were  so  far  sat- 

22  Microscopy. 


338  HOW   TO   SEE   WITH  THE   MICROSCOPE. 

isfactory  as  to  lead  to  the  employment  of  the  approxi- 
mate tabes  in  his  general  practice ;  and  the  degree  of 
accuracy  afforded  by  the  use  of  these  tubes  is  quite  equal 
to  the  ordinary  demands  of  the  medical  profession. 
The  principal  source  of  error  arises,  as  we  believe,  from 
the  fact  that  the  coagulated  albumen  will  at  times  pack 
•closer  in  the  tube  than  at  others.  By  using  three  or 
four  tubes  in  one  and  the  same  analysis,  taking  the 
mean  of  the  results,  the  approximate  process  will,  in 
most  instances,  be  all  that  can  be  desired.  Proceed  as 
follows: 

In  a  clean  evaporating  dish,  or  a  Florence  flask,  coag- 
ulate by  heat  three  fluid  ounces  of  the  urine  to  be 
tested;  set  aside  until  nearly  cold;  shake,  well;  now 
take  three  marais  tubes,  fill  the  first  full,  also  the 
second  with  the  treated  urine  and  coagulum ;  pour  the 
Temainder  into  the  third  tube,  rinsing  the  dish  with  a 
little  water,  adding  the  wash  to  the  several  tubes.  The 
three  tubes  can  be  thus  made  to  contain  the  entire 
coagulum  from  the  three  ounces  of  urine;  set  aside  for 
twenty-four  hours,  after  which  time  read  the  several 
tubes ;  add  the  readings  together  and  divide  by  three, 
and  every  two  whole  cubic  centimetres  will  represent 
one  grain  of  albumen  to  the  ounce  of  urine. 

In  the  daily  routine  it  will  often  suffice  to  use  but 
one  tube,  in  which  case  all  that  is  necessary  will  be  to 
coagulate  a  single  fluid  ounce  of  the  urine;  when  cool, 
shake,  and  pour  into  the  approximate  tube,  rinsing  the 
dish  as  before,  adding  the  wash  to  the  tube ;  at  the  end 
of  twenty-four  hours  read  off  the  amount  of  coagulum ; 


APPARATUS.  339 

every  two  whole  c.  c.  will  equal  one  grain  of  albumen 
to  the  ounce  of  albumen. 

Reaction. — Urines  being  at  times  either  acid,  neutral, 
or  alkaline,  it  is  often  interesting,  not  only  to  observe 
as  to  the  fact,  but  also  as  to  the  degree  of  acidity  or 
alkalinity;  to  accomplish  this  prepare  the  following 
solutions: 

Test  Solution  for  Acidity. — In  1,000  grains  of  dis- 
tilled water  dissolve  ten  grains  of  pure  hydrate  of  soda. 

Test  Solution  for  Alkalinity  . — In  1,000  grains  of 
distilled  water  dissolve  15.75  grains  of  pure  oxalic  acid. 
Equal  volumes  of  these  two  solutions  will  exactly  neu- 
tralize each  other. 

To  Test  the  Degree  of  Acidity  in  a  Sample  of  Urine. 
— Fill  the  burette  with  the  soda  solution ;  measure  one- 
halt  fluid  ounce  of  the  urine  into  a  wine-glass ;  deliver 
the  soda  from  the  burette  into  this  a  few  drops  at  a 
time,  stirring  well  after  each  addition  and  testing  with 
litmus  paper;  when  the  mixture  fails  to  affect  the 
latter,  read  the  burette  twice,  the  figures  read  will  indi- 
cate the  number  of  grains  of  the  solution  employed 
required  to  neutralize  a  fluid  ounce  of  the  urine.  To 
test  for  alkalinity  proceed  as  above,  using  the  acid  solu- 
tion in  place  of  the  soda,  and  also  red  litmus  paper  in 
place  of  the  blue.  The  daily  variations  in  any  particu- 
lar case  can  in  this  manner  be  determined  and  recorded. 

Proportion  per  tluid  Ounce  of  certain  of  the  Urinary 
Constituents. 

The  estimates  given  in  this  part  of  the  table  are  roughly  ap- 
proximative, and  represent  the  widest  variations  consistent  with 


340 


HOW   TO   SEE   WITH   THE   MICROSCOPE. 


normal  conditions.    The  variations,  always  considerable,  are 
particularly  marked  as  regards  the  uric  acid . 

Urea 6'50  to  10'50  grains. 

Chlorine  (1*30  to  3'60  s rs.  of  chloride  of  sodium) 0'80    "  2'15 

Sulphuric  acid  (1-30  to  3'20  grs.  of  sulphates)    0'66    "  T62       ** 

Phosphoric  acid  (2- 10  to  4'00  grs.  of  phosphates) 1'17    »•  2'25       " 

Do         do    combined  with  alkalies  (phosphate  of 

soda  and  phosphate  of  magnesia) 0'78    **  T40       " 

Do  do  combined  with  earths  (phosphate  of 
lime  and  ammonio-magnesian  phos- 
phate)   0-39  "  0'85  * 

Uric  acid  (0.40  to  0-70  grs.  of  urates) 0'23    "  0'40       " 


TABLE  FOB  REDUCING  THE  INDICATIONS  OP  A  GLASS  UBINOMETEB  TO 
STANDARD  TEMPERATURE  (60°  Fahr.)  WHEN  THE  SPECIFIC  GRAVITY  HAS 

BEEN  TAKEN  AT    A    HIGHER    TEMPERATURE.      (BlHD,    Urinary  Deposits. 

etc.,  Philadelphia,  1859  p.  7J.) 


Tempera- 
ture and 
degree. 

60 

61 

62 

63 

64 

95 

66 


No.  to  be 
added  to 
the  indi- 
cation. 

o-oo 

0-08 
0-16 
0-24 
0-32 
0-40 
0'50 


0-70 


Tempera- 
ture and 
degree. 

No,  to  be 
added  to 
the  indi- 
cation. 

Tempera- 
ture and 
degree. 

No.  to  be 
added  to 
the  indi- 
cation. 

69 

0-80 

78 

1-70 

70 

0.90 

79 

1-80 

71 

1-00 

80 

1-90 

72 

1-10 

81 

2-00 

73 

1-20 

82 

2-10 

74 

1-30 

83 

2-20 

75 

1-40 

84 

2-30 

76 

1-50 

85 

2-40 

77 


1-60 


APPENDIX. 


As  a  matter  of  convenience  to  the  student  we  present 
the  addresses  of  American  dealers  in  Microscope  Stands, 
Objectives,  etc.  The  list  is  compiled  from  the  various 
catalogues  and  other  sources  of  information  which  hap- 
pened to  be  in  our  possession.  It  is  therefore  probably 
incomplete,  but  nevertheless  will  be  found  to  comprise 
most,  if  not  all  of  the  leading  dealers.  Of  the  latter, 
those  marked  with  an  Asterisk  (*)  issue  illustrated  cat- 
alogues, which  can  be  obtained  on  application,  free  of 
expense : 

NAMES  AND  ADDRESS  OF  DEALERS  IN  MICROSCOPES,  OBJECT- 
IVES, ETC.,  ALPHABETICALLY  ARRANGED. 

(*)Bausch  &  Lomb  Optical  Company,  37  Maiden 
Lane,  New  York;  factory  at  Rochester,  New  York. 

(*)R.  &  J.  Beck,  (London);  American  Agency  in 
charge  of  W.  H.  Walmsley,  Chestnut  street,  Philadel- 
phia, Pa. 

(*)W.  H.  Bulloch,  126  Clark  street,  Chicago,  111. 

F.  J.  Emmerich  (Importer),  38  Maiden  Lane,  New 
York. 

E.  Gundlach,  L.  R.  Sextcn,  agent,  Rochester,  New 
York. 

(*)T.  H.  McAllister,  49  Nassau  street,  New  York. 

Pike  (Dealer),  518  Broadway,  New  York. 

341 


342  HOW  TO   SEE   WITH   THE   MICROSCOPE. 

(*)James  W.  Queen  &  Co.,  924  Chestnut  street,  Phil- 
adelphia, Pa. 

William  A.  Kogers  (Micrometer  Plates,  etc.,)  Cam- 
bridge, Mass. 

(*)Messrs.  C.  A.  Spencer  &  Sons,  (Objectives,  Ac- 
cessories, etc.,)  Geneva  New  York. 

L.  Schraner,  50  Chatham  street,  New  York. 

(*)J.  W.  Sidle  &  Co.,  Lancaster,  Pa. 

(*)Robert  B.  Tolles,  Hanover  street,  Boston,  Mass. 
Charles  Stodder,  Agent,  Devonshire  street,  Boston, 
Mass. 

(*)George  Wale,  Patterson,  N.  J.  George  Wale  & 
Co.,  Hoboken,  N.  J.,  Agents. 

(*)  William  Wales,  Fort  Lee,  New  Jersey. 

(*)Joseph  Zentmayer,  147  South  Fourth  street,  Phil- 
adelphia, Pa. 

The  following  price  list  of  stands,  etc.,  is  only  in- 
tended to  include  those  previously  described  in  this 
book.  Several  of  the  makers  therein  mentioned  manu- 
facture various  models  not  included  in  our  list.  The 
stands  ot  the  Messrs.  Spencer's  have  been  intention- 
ally omitted,  as  we  learn  that  they  are  now  devoting 
their  entire  attention  to  the  production  of  objectives. 

The  list  of  objectives  is  similarly  incomplete.  With 
the  glasses  of  Messrs.  Tolles  and  Spencer  we  have  had  a 
large  experience.  Several  months  ago  the  Messrs.  Bausch 
&  Lomb  sent  us  a  line  of  their  objectives  for  study, 
all  of  which,  after  working  with  the  same  more  or  less 
for  nearly  a  year,  proved  reliable  glasses  for  their  cost. 


APPENDIX.  343 

The  entire  list  may  be  understood  to  include  only  such 
objectives  as  we  have  used  to  a  greater  or  less  extent 
in  practical  work,  and  of  which  we  can  therefore  speak 
from  experience,  and  without  prejudice  to  other  reliable 
makers. 

We  earnestly  advise  the  student  contemplating  the 
purchase  of  object  glasses,  especially  when  ordering 
the  same  to  be  made  by  the  optician,  to  seek  the  advice 
of  some  expert  friend.  Protection  is  thus  afforded  both 
to  the  maker  and  the  buyer,  and  it  has  often  happened 
that  the  latter,  through  sheer  incompetency,  returns  a 
really  fine  glass  to  its  maker,  with  the  assertion  that  it 
has  proved  unsatisfactory.  While  on  the  other  hand, 
especially  in  glasses  of  high  balsam  angles,  there  IS  a 
choice  in  the  work  of  the  very  best  makers.  The  ex- 
pert, too,  will  render  valuable  assistance  in  specifying 
the  exact  kind  of  objective  desired. 

MICROSCOPE   STANDS,   BY  W.   H.  BULLOCH,  NO.  126 
CLARK  STREET,  CHICAGO,  ILL. 

Large  best  stand,  Al,  binocular,  iris  diaphragn,  with  the 

latest  improvements,  draw-tube,  5  eye  pieces $300  00 

Same  as  above,  but  monocular,  iris  diaphragm,  with  three 

eye  pieces 250  00 

Polished  mahogany  case,  with  side  case  for  accessories.  25  00 
Small  best  stand,  A.  B.,  binocular,  4  eye  pieces  and  iris 

diaphragm 225  00 

Monocular,  two  eye  pieces  and  iris  diaphragm 175  00 

Polished  mahogony  case 20  00 

" D  "  stand,  all  brass,  2  eye  pieces  and  case 75  00 

" D  "  stand,  all  brass  except  the  base,  2  eye  pieces  and 

case..,                 67  00 


344  HOW   TO    SEE   WITH   THE    MICROSCOPE. 


MICROSCOPES  AND  OBJECTIVES  BY  THE  BAUSCH  & 
LOMB  OPTICAL  COMPANY. 

The  Professional  Microscope,  with  the  following  acces- 
sories :  Hemispherical  immersion  condenser  and  ob- 
lique light  projector,  plain  and  concave  mirrors,  sub- 
stage,  receiving  accessories  of  standard  English  size, 
two  revolving  diaphragms,  sub-stage  with  internal 
*'  society  screw,"  2  slot  diaphragms  for  mirror,  3  Gund- 
lach's  periscopic  eye  pieces  (B,  C  and  D),  four  object- 
ives, viz :  2-inch,  l-5th  inch,  3-4th  inch  and  l-8th  inch 
immersion,  with  adjustment  for  cover,  magnifying 
powers  from  30  to  800  diameters,  eye  piece  micrometer, 
camera  lucida,  bull's  eye  condenser,  the  whole  in 
upright  walnut  case,  with  handle,  lock  and  key,  and 
drawer  for  accessories $200  00 

Large  Student's  Microscope,  plain  and  concave  mirrors, 
sub-stage  of  extra  size  to  receive  standards,  English 
accessories,  revolving  diaphragm,  etc.,  all  attached  to 
the  swinging  mirror  bar ;  sub-stage  and  mirror  are  re- 
movable ;  three  eye  pieces,  A,  B  and  C,  three  object- 
ives, 2-inch,  3-4th  inch  and  t-5th  inch,  magifying  from 
22  to  375  diameters,  eye  piece,  micrometer,  camera 
lucida,  in  upright  walnut  case,  with  handle,  lock  and 
key,  and  drawer  for  accessories 90  00 

Family  Microscope,  concave  mirror,  adjustable  for  ob- 
lique light,  one  (B)  eye  piece,  one  first-class  achromatic 
objective  (one-half  inch  dividing)  powers,  50  and  100 
diameters,  in  upright  walnut  case,  with  handle,  lock 
and  key 20  00 

The  Messrs.  Bausch  &  Lomb  have  brought  out  a  new  model 
which  they  term  the  Physicians'  Stand,  which  may  be  thus  de- 
scribed : 

Large,  heavy  cast  iron  foot,  rack  and  pinion  for  coarse 
adjustment,  draw-tube,  allowing  2  1-2-inches  shorten- 
ing, fine  adjustment  by  a  new  friclionless  motion,  large 
hard  rubber  stage,  sub-stage  of  standard  size,  carrying 


APPENDIX.  345 

three  diaphragms,  which,  when  pushed  up,  will  closely 
reach  the  object  slide,  plain  and  concave  mirrors,  ar- 
ranged so  that  their  distance  from  the  object  may  be 
varied,  2  eye  pieces,  A.  and  C,  2  objectives,  3-4ths  inch 
and  l-5th  inch,  magnifying  powers,  when  the  tubes  are 
completely  drawn  out,  from  50  to  375  diameters,  eye 
piece,  micrometer  and  camera  lucida,  in  upright  wal- 
nut case,  with  lock  and  key 60  00 

The  past  twelve-month  has  witnessed  unusual  activity  on  the 
part  of:  microscope  makers.  Mr.  Zentmayer,  in  the  production 
of  his  "  Histological,"  (as  also  the  advent  of  the  Acme  Stand) 
stimulated  other  makers  to  increased  energy  in  the  production 
of  small,  low-priced  and  reliable  stands  capable  of  performing 
the  work.of  larger  and  costly  instruments. 

At  the  late  (August,  1880)  meeting  of  the  American  Society 
of  Microscopists,  held  at  Detroit,  Michigan,  two  medium-priced 
stands  were  exhibited  which  were  regarded  bv  competent 
judges  as  being  quite  equal  to  the  Acme  Stand.  One  of  these 
was  made  by  Mr.  Bullock,  of  Chicago,  and  its  cost — as  near  as 
I  can  learn—  will  be  about  $50. 

The  other  stand  referred  to  was  exhibited  by  the  Messrs. 
Bausch  &  Lomb,  of  Rochester,  N.  Y.  It  is  called  the  tw  Inves- 
tigator." Messrs.  B.  &  L,  have  furnished  the  author  with  the 
following  description  of 

THE  INVESTIGATOR  MICROSCOPE. 

In  this  stand  we  confidently  claim  to  have  reached  a  higher 
degree  of  perfection  than  is  possessed  by  any  one  approximat- 
ing it  in  price.  We  have  combined  in  it  the  qualities  of  a 
first-class  and  high-priced  stand,  and  at  no  sacrifice  of  its 
working  qualities.  The  different  parts  are  ingeniously  com- 
bined, are  strong  and  firm,  and  in  the  parts  subject  to  friction 
we  have  introduced,  as  much  as  possible,  new  compensating 
bearings,  which  insure  the  retention  of  smooth  and  reliable 
movements  with  any  amount  of  work.  Working  microscopists 
will  understand  the  value  of  this  quality.  When  contracted  it 
stands  but  11  high,  but  can  be  extended  to  18  inches. 


346  HOAV   TO   SEE   WITH  THE   MICROSCOPE. 

The  base  is  of  the  tripod  form,  neatly  japanned ;  pillar  and 
arm  of  brass,  connected  by  a  solid  joint,  which  allows  inclina- 
tion of  body  to  any  angle;  rack  and  pinion  for  coarse  adjust- 
ment, tine  adjustment  by  our  patent  frictionless  motion  ;  main 
tube  with  two  draw  tubes.  This  is  an  entirely  new  feature  in 
microscopes,  which  is  an  unquestionable  improvement.  It  per- 
mits the  use  of  standard  length  of  tube  for  quick  adjustment 
in  outside  tube,  same  as  in  instruments  without  rack  and  pinion 
adjustment ;  the  same  for  any  low  power  objective  and  the  use 
of  amplifier  in  either  combination.  The  outside  tube  has  ,a 
broad  gauged  screw,  and  adapter  with  society  screw.  The  stage 
lies  in  the  same  plane  as  center  of  movement  for  mirror,  is  of 
brass,  and  has  concentric,  revolving  motion  with  removable 
clips.  It  is  thin  to  allow  great  obliquty,  and  as  it  rests  upon  a 
strong  projecting  arm,  is  perfectly  firm  under  any  manipulation. 

The  mirror  bar  swings  with  a  perfectly  easy  but  firm  motion, 
upon  one  bearing  to  any  obliquity  below,  and  above  the  stage 
for  the  illumination  of  opaque  objects,  and  has  affixed  to  it  a 
secondary  bar,  to  which  the  mirror  is  attached  and  which  allows 
the  separate  use  of  the  latter  in  any  position  of  the  sub-stage. 
It  is  provided  with  a  sliding  arrangement,  whereby  the  mirror 
may  be  moved  to  and  from  the  object.  The  mirrors  are  plain 
and  concave,  and  of  large  size.  The  substage  is  adjustable 
along  the  mirror  bar,  and  entire  removable.  It  contains  a 
diaphragm  which  may  be  brought  directly  under  the  stage.  The- 
ring  is  of  standard  size  and  is  easily  centered  by  a  set  screw. 
The  stand  is  furnished  with  an  eye  piece  of  any  power. 

In  black  walnut  case,  with  receptacles  for  eye  pieces  and 
objectives,  drawer  for  accessories,  handle  and  lock,  price  $40.00. 

Same,  with  C  Eye  Piece,  arranged  for  micrometer,  camera 
lucida,  micrometer,  3-4  inch  and  1-5  inch  objectives,  $65.00. 

BAUSCH  &  LOME  OBJECTIVES. 

Deg.  Price. 

2inch 18 $1200 

2inch 12 600 

linch 36  2000 

linen. .                          20 6  (K> 


APPENDIX.  347 

Deg.  Price. 

3-4inch 27 800 

l-2inch 72  2200 

1-2  inch 40  9  00 

4-10 100  20  00 

3-10 75  11  00 

1-4 100  .', 14  00 

1-5 108  1500 

1-6  inch 180  Adjusting 30  00 

1-8 Immersion 180  Adjusting 4000 

MICROSCOPES  OF  THE  MESSRS.  R.  &  J.  BECK,  OF 
LONDON.  AMERICAN  AGENCY  IN  CHARGE  OF 
W.  H.  WALMSLEY,  ESQ  ,  1016  CHESTNUT  STREET, 
PHILADELPHIA,  PA. 

Popular  Microscope  stand,  binocular,  with  one  pair  of 
eye  pieces,  concave  mirror,  diaphragm,  forceps,  glass 
plate,  pliers,  etc $6500 

Same,  but  monocular 40  00 

Economic  Microscope,  as  furnished  by  the  makers,  mo- 
nocular, with  sliding  coarse  adjustment,  1  inch  and 
1-4  inch  object  glasses,  1  eye  piece,  concave  mirror, 
condensing  lens,  glass  plate  with  ledge,  brass  pliers 
and  diaphragm,  in  mahogany  case 35  00 

The  same,  with  rack  and  pinion,  for  coarse  adjustment, 
concave  and  plane  mirrois,  stage  forceps,  etc.,  in  ma- 
hogany case 50  00 

(Both  of  the  above  stands  are  fitted  with  fine  adjust- 
ment screw.) 

Extra  eye  pieces,  each 4  00 

The  Messrs.  Beck  have  just  published  a  large  and  com- 
plete illustrated  catalogue  of  their  microocopes  and 
other  scientific  instruments,  which  they  furnish  to  any 
one  on  application.  Among  their  later  models  of  mi- 
croscope stands  we  notice  the  u  New  National,"  cost- 
ing, with  one  eye  piece,  concave  and  plane  mirrors, 
diaphragm,  stage  forceps,  glass  plate  pliers,  etc 40  00 

Mahogany  cabinet  for  the  same 10  00 


348  HOW   TO    SEE   WITH   THE    MICROSCOPE. 

Since  the  chapter  on  stands  was  written  we  have  received  the 
following  description  of 

BECK'S  INTERNATIONAL  MICROSCOPE    STAND. 

The  improved  large  best  or  international  microscope  stand 
has  a  tripod  (A)  for  its  base,  upon  which  is  placed  a  revolving 
fitting  (B),  graduated  to  degrees,  by  which  means  the  micro- 
scope can  be  turned  round  without  its  being  lifted  from  the 
table,  and  the  amount  of  such  rotation  registered ;  upon  this 
fitting  two  pillars  are  firmly  fixed,  and  between  them  the  limb 
<C)  can  be  elevated  or  depressed  to  any  angle,  and  tightened  in 
its  position  by  the  lever  (D).  The  limb  carries  atone  end  the 
body  (E)  (binocular  or  monocular)  with  eye-pieces  and  object- 
glasses;  in  its  centre  the  compound  stage  (F),  beneath  which  is 
the  circular  plate,  sliding  on  a  dove-tailed  fitting,  and  moved  up 
and  down  by  the  lever  (Z),  and  cany  ing  the  supplementary  body 
or  sub-stage  (G);  and  at  the  lower  end  a  triangular  bar  carrying 
the  mirror  (H).  Each  of  these  parts  requires  a  separate 
description. 

The  binocular  body  consists  of  two  tubes,  the  one  fitted  in  the 
optical  axis  of  the  microscope,  and  the  other  oblique.  At  their 
lower  end  and  immediately  above  the  object-glass  there  is  an 
opening,  into  which  a  small  brass  box  or,  fitting  (I)  slides ;  this 
box  holds  a  prism  so  constructed  that  when  slid  in  it  intercepts 
half  the  rays  from  the  object-glass,  diverts  them  from  their 
direct  course,  and  reflects  them  into  the  additonal  or  oblique 
tube.  To  the  prism-box  is  attached  a  spring-catch,  which.when 
pressed  in,  permits  of  the  removal  of  the  prism-box  ;  but  this  is 
only  needed  for  cleaning,  as,  when  the  box  is  drawn  back  to  the 
distance  allowed  by  this  spring,  the  prism  in  no  way  interferes 
with  the  field  of  view,  and  all  the  rays  pass  up  the  direct  body, 
and  the  microscope  is  converted  into  a  monocular  one. 

The  upper  or  eye-piece  ends  of  the  tubes  are  fitted  with  racks 
and  pinion  for  varying  the  distances  between  the  two  eye-pieces 
to  suit  the  differences  between  the  eyes  of  various  persons  ;  and 
arrangements  are  made  for  racking  out  one  tube  more  than  the 
other,  to  suit  irregularities  or  inequalities  between  the  eyes  of 
the  observer. 
This  body  is  moved  up  and  down  with  a  quick  movement  by 


APPENDIX.  349 

means  of  the  milled  heads  (K),  and  with  a  very  delicate  and  fine 
adjustment  by  the  milled  head  (L).  This  milled  head  works 
against  a  lever,  which  moves  a  slide  independent  of  the  rack- 
movement,  and  gives  an  adjustment  at  once  certain  and 
decided. 

The  compound  stage  is  of  an  entirely  new  construction :  the 
object  is  most  frequently  merely  placed  upon  it,  but,  if  neces- 
sary, it  can  be  clamped  by  carefully  bringing  down  the  spring- 
piece  (M),  the  ledge  will  slide  up  or  down,  and  the  object  may 
be  pushed  sideways;  this  arrangement  forms  the  coarse  adjust- 
ment. Finer  movements  in  vertical  and  horizontal  directions 
are  effected  by  means  of  two  milled  heads  (N"  and  O),  the  screws 
attached  to  which  are  kept  up  to  their  \vork  by  opposing  springs 
so  as  to  avoid  all  strain  or  loss  of  time.  The  whole  stage 
revolves  in  a  circular  ring  by  the  milled  head  (P),  or  this  can  be 
drawn  out,  and  then  it  turns  rapidly  by  merely  applying  the  fin- 
gers to  the  two  ivory  studs  (Q  Q)  fastened  to  the  top  plate, 
which  is  divided  into  degrees  to  register  the  amount  of  revolu- 
tion. The  stage  is  attached  to  the  limb  on  a  pivot,  and  can  be 
rotated  to  any  angle,  which  angle  is  recorded  on  the  divided 
plate  (R),  or  can  be  turned  completely  over,  so  that  the  object 
can  be  viewed  by  light  of  any  obliquity  without  any  interfer- 
ence from  the  thickness  of  the  stage. 

Beneath  and  attached  to  the  stage  is  an  iris  diaphragm  (S), 
which  can  be  altogether  removed,  as  shown  in  the  illustration, 
from  its  dove-tailed  fitting,  so  as  not  to  interfere  during  the 
rotation  of  the  stage.  The  variations  in  the  aperture  of  this 
diaphragm  are  made  by  a  pinion  working  into  a  racked  arc  and 
adjusted  by  the  milled  head  (T). 

Beneath  the  stage  are  two  triangular  bars  (U  Y),  the  one 
revolving  round  and  the  ocher  rigid  in  the  optical  axis  of  the 
instrument.  On  the  former  the  sub-stage  (G),  carrying  all  the 
apparatus  hereafter  described  for  illumination  and  polarization, 
fits,  and  is  racked  up  and  down  by  the  milled  head(\V);  the 
mirror  also,  if  desired,  slides  on  the  same  bar ;  the  revolving 
motion  to  this  bar  is  given  by  the  milled  head  (X),  and  the 
amount  of  angular  movement  is  recorded  on  the  circle  (Y), 
whilst  the  whole  of  this  part  of  the  stand  is  raised  and  lowered 


350  HOW   TO    SEE    WITH   THE    MICROSCOPE. 

concentric  with  the  optical  axis  of  the  instrument  by  the  lever 
(Z),and  the  amount  of  such  elevation  or  depression  is  registered 
on  a  scale  attached  to  the  limb.  This  bar  can  be  carried  round 
and  above  the  stage,  and  be  thus  used  for  opaque  illumination. 

The  lower  triangle  bar  (V)  carries  the  mirror  (H),  or  a  right- 
angle  prism,  when  the  illumination  is  required  to  be  concentric 
with  the  optical  axis  of  the  instrument,  and  independent  of  the 
movements  of  other  illuminating  aparatus. 

The  mirror- box  contains  two  mirrors,  one  flat  and  the  other 
concave ;  it  swings  in  a  rotating  semi-circle  attached  to  a 
lengthening  bar,  which  enables  it  to  be  turned  from  one  side  to 
the  other,  and  revolves  on  a  circular  ti tting  for  giving  greater 
lacilities  in  regulating  the  direction  of  the  beam  of  light 
reflected,  the  whole  sliding  upon  either  of  the  triangle  bars,  pre- 
viously referred  to,  and  made  to  reverse  in  the  socket  (a)  so  as 
to  bring  the  centre  of  the  mirror  concentric  with  the  axis  of  the 
microscope  in  either  case. 

As  the  mirror  alone  is  insufficient  for  many  kinds  of  illumin- 
ation, some  provision  h;is  to  be  made  for  holding  various  pieces 
of  apparatus  between  ther  object  and  the  mirror.  For  this  pur- 
pose a  supplementary  body,  or  sub-stage,  is  mounted  perfectly 
true  with  the  body,  and  is  moved  up  and  down  in  its  fitting  by 
rack  and  pinion  connected  with  the  milled  heads  (W).  This 
sub-stage,  to  which  reference  has  already  been  made,  is  now  re- 
garded as  one  of  the  most  important  parts  of  the  achromatic 
microscope;  in  it  all  the  varied  appliances  for  modifying  the  char- 
acter and  direction  of  the  light  are  fitted.  But  a  few  years  since 
it  was  considered  sufficient  for  this  part  of  the  stand  to  be  con- 
structed so  as  to  move  up  and  down  perfectly  coincident  with 
the  optical  axis  of  the  instrument,  and  for  that  purpose  it  was 
racked  in  a  groove  planed  out  on  the  same  limb  as  that  on  the 
upper  end  of  which  the  optical  portions  were  carried.  But  latelv 
microscopists  have  shown  the  desirability  of  affording  every 
facility  for  lateral  angular  adjustments  ;  and  this  has  led  to  the 
sub-stage  being  attached  to  an  arc  (b)  working  in  tbe  circular 
plate  (Y),  and  moved  by  a  rack  and  pinion  (X),  whilst  the 
amount  of  such  angular  movement  is  recorded  on  the  upper  sur- 
face of  the  plate  (Y).  Having  once  fixed  the  angular  direction 


APPENDIX.  351 

of  the  light,  the  focussing  of  it  depends  upon  the  lever  (Z), 
which  moves  the  circle  up  and  down,  and  with  it  the  arm  carry- 
ing the  illuminating  apparatus  in  the  optical  axis  of  the  instru- 
ment. So  long  ago  as  1854  Mr.  Grubb,  of  Dublin,  called  atten- 
tion to  the  advantage  of  mounting  the  illuminating  apparatus 
on  a  revolving  arm  or  arc,  which  he  thus  describes  in  his  pro- 
visional specification  for  improvements  in  microscopes.  No. 
1477,  5th  July,  1854  :— k>  My  third  improvement  consists  in  the 
addition  of  a  graduated  sectorial  arc  to  microscope  concentric 
to  the  plane  of  the  object  "  in,  situ,"'  on  which  either  the  afore- 
said prism  or  other  suitable  illuminator  is  made  to  slide,  thereby 
producing  every  kind  of  illumination  required  for  microscopic 
examination,  and  also  the  means  of  registering  or  applying  any 
definite  angle  of  illumination  at  pleasure."  With  but  slight 
modification,  this  is  the  plan  adopted  in  this  stand. 

The  sub-stage  is  also  fitted  with  complete  centering  and  rotat- 
ing adjustments,  the  latter  having  a  graduated  circle  attached, 
and  fittings  for  carrying  Barker's  series  of  selenites,  blue  glass 
disks  for  modifying  the  light,  etc.  In  all  the  requirements  of  an 
instrument  of  precision,  and  fully  meeting  the  wants  of  the 
most  advanced  modern  workers,  it  is  confidently  believed  that 
this  new  stand  has  no  rival. 

The  price  of  the  International  Stand,  Binocular,  with  five  eye- 
pieces, concave  and  plane  mirrors,  and  right  angle  prism,  stage 
forceps,  pliers  and  glass  plate  with  ledge,  is  .  .  $325.00 

The  price  of  the  International  Stand,  Monocular,  with  three 
«ye-pieces,  and  the  same  fittings  as  above,  is,  .  .  $275.00 

(The  Messrs.  Beck  manufacture  several  grades  of  objectives, 
as  will  be  seen  by  reference  to  their  published  catalogue.) 

J.  W.  SIDLE     &  CO.,  LANCASTER,  PA.,  ACME  MICRO- 
SCOPES AND  ACCESSORIES. 

We   here  quote  the  prices  of  the  Acmes,  and  a  few  of    the 

more  important  accessories. 

3a.  Acme  Monocular,  with  brass  tripod  base,  rotating 
stage,  iris  diaphragm  and  substage  fitting  with  Society 
screw  for  using  objectives  as  condensers ;  in  walnut 
case  with  lock  and  handle,  and  drawer  for  accessories,  $  50.00 


352  HOW   TO    SEE    WITH   THE   MICROSCOPE. 

36.  Acme  Binocular,  with  one  pair  oculars,  and  outfit  as 
above 75.00 

3c.  Acme  Monocular,  as  above,  with  i  objective  of  32° 
and  i  of  100°,  and  small  bull's  eye  condenser,  .  .  75.00 

3d.  Acme  Binocular,  as  above,  with  f  of  32°,  i  of  100° 
and  bull's  eye,  -.•' 100.00 

2a.  Large  Acme  Monocular,  r6tating  glass  stage,  sub- 
stage,  with  rack  and  pinion,  in  polished  mahogany  case 
with  side  case  for  accessories, 100.00 

26.  Large  Acme  Binocular,  same  as  above,with  addition- 
al nose-piece,  as  per  circular,  .  .  .  .  .  135.00 

2c.  Large  Acme  Monocular,  as  above,  with  mechanical 
stage  and  2  pair  oculars, 135.00 

2cZ.  Large  Acme  Binocular,  as  above,  with  mechanical 
stage  and  2  pair  oculars,  .  .  .  .  *  «  170.00 

PRICES  OF  ACCESSORIES. 

Mechanical  stage  for  Acme  No.  3,          ....       $16.00 
Walnut  base  with  lamp  and  adjustable  stand,  with  brass 
fitting  to  receive  lower  end  of  pillar,  converting  the  Ac- 
me into  a  Class  Microscope,     .       *       .       .    ;   .       .       5.50 
Camera  Lucida,          .       .       .       v       *       .       .       .  5.50 

Neutral  Tint  (Beale's)^         .       *       ..    <.       -.       ;       .       3.00 

Iris  Diaphragm,  .' 4.50 

Sub-stage  fitting  for  using  objectives  as  condensers,       .       l.Oi) 

Woodward's  prism,  unmounted, 1.50 

"  "       mounted  to  screw  in  stage,       .       .       4  00 

Mechanical  Stage, «.  •      25.00 

Sliding  Object  Carrier,  fitted  to  stand,       .       .       .       .       4.00 

Paraboloid,  plain, i       .    '  .          8.50 

Parabolic  Illuminator, "    .       .       8.50 

Polarizer  for  Acme,  selenite  screwing  in  stage,  to  rotate 

independently  of  Nichol  prism, 13.50 

Polarizer,  best,  with  large  prism, 18.00 

Mechanical  Finger, 6.50 

Solid  Ocular,  i,  i,  i  inch, 8.00 


APPENDIX.  353 


CONGRESS  TURN  TABLE. 

This   table   has   made   a  reputation   for  itself.    Retail 
price $6.50 

PRICES   OF  ACME  SERIES  OF  OBJECTIVES. 

2    inch,    15°    ...    $13.00      ' 3-10  inch,  115°  non  adjust- 
able,   .    .    $16.00 
H    "        18°    ...      14.00       3-10    u      115°  adjustable,    20.00 

1  "        36°    ...     15.00       1-4      "      100°  non-adjust- 

able,   .    .      14.00 

f     "        32°    ...      12.00       1-5      "      120°  non-adjust- 
able,     .    .    16.00 

f     "        36°    ...      15.00       1-5      "      120°  adjustable,    20.00 
|     •*•        60°    ...      14.00          Other  lenses  quoted  in 

Catalogue. 

MICROSCOPE  OBJECTIVES,  BY  MESSRS.  C.  A.  SPENCER 
&  SONS,  GENEVA,  N.  Y. 

FIRST  CLASS. 

Size.                                               Deg.  Price. 

3inch 13  $1800 

2  inch.. 20  2500 

1  inch 50  4500 

2-3inch 47  3200 

1-2  inch 100  Adjustable 50  00 

1-4  inch,  dry  and  immersion  180        6500 

1-6  inch,    "                  "           180        7000 

1-8  inch,    "                  u          180        7000 

l-lOinch,u                  "          180        8000 

1-16  inch,"                  "          180        11500 

PROFESSIONAL  SERIES. 

3inch 13  $1800 

2inch 16  1800 

1  inch 33  1800 

2-3inch 36  2000 

23  Microscopy. 


354  HOW   TO    SEE    WITH   THE   MICROSCOPE. 

1-2  inch  .   65 2500 

1-4  inch,  Adjustable 115  24  00 

1-6  inch,  "         175  Dry  and  immersion 3400 

1-8  inch,  "         175     u  "          40  00 

1-15  inch,         "         175     "  "          50  00 

STUDENTS'  SEBIES. 

3  inch 8 $6  00 

2  inch 10 6  00 

linch 22 1000 

2-3  inch 32 , 1200 

l-2inch 50 1500 

1-4  inch 100 16  00 

1-8  inch 135 25  00 

"Wenham's  Reflex  Illuminator 10  00 

(The  Messrs.  Spencer  &  Sons  furnish  a  full  line  of  goods  desir- 
able by  the  microscopist,  such  as  solid  eye  pieces  camera  lucidas, 
and  accessories  generally.  Their  former  connection  with  the 
Optical  Company  has  been  dissolved,  and  they  now  continue 
business  on  their  own  account,  as  above  stated,  at  Geneva,  1ST.  Y.) 

MICROSCOPES  AND  OBJECTIVES,  BY  R.  B.  TOLLES, 
BOSTON,  MASS. 

Tolles'  Large  Microscope,  •'  B,"  no  objectives $225  00 

Student's  stand,  1  inch  E.  P.,  1,  and  l-4th  inch  object- 
ives, packed  in  black  walnut  case 50  00 

Additions,  etc.,  to  the  above- 
Extra  eye  pieces,  each 4  00 

Camera  lucida 5  00 

Sub-stage,  for  accessory  apparatus 5  00 

Sliding  stage,  giving  horizontal  and  vertical  movements 

by  hand 15  00 

Fine  adjustment  by  lever  and  micrometer  screw 20  00 

Rack  and  pinion  for  coarse  ad j  ustment 12  00 

Draw  tube 4  00 

Plain  mirror 3  00 

Thin  glass  stage  to  rotate  on  the  optical  axis 10  00 

Packing  boxes  for  transportation,  extra 1  00 


APPENDIX.  355 

Student's  Microscope,  with  one  inch  and  one  -  fourth 
inch  objectives  (second  quality)  one  ocular,  rack  and 
pinion,  lever,  fine  adjustment  for  focus,  sub-stage  for 
Illuminating  apparatus,  revolving  diaphragm,  plain 
and  concave  mirrors,  side  stand  for  illuminating 

opaque  objects,  black  walnut  case 90  00 

TOLLES'  FIRST  CLASS  OBJECTIVES. 

Size                                                         Degrees.  Price. 

1-2  inch,  Angle  apertured 60  to   90 $4000 

4-10                                        ....    90  to  120  4500 

4-10               u             ik         135  to  145 6500 

1-4  or  1-5      u             "         ....  120  to  130 4500 

1-4                "             -         ....              150 55  00 

1-4                4-             l-         180  70  00 

1-6                '•             lt         180 75  00 

1-8                 "             "         180 80  00 

1-10               "             "          ....              180 85  00 

TOLLES'  PATENT  SOLID  EYE  PIECES. 

l-2inch,"D" $800 

1-4  inch 8  00 

Either  of  the  above,  for  his  Student's  Microscope 6  00 

Wenham's  Reflex  Illuminator 1000 

MICROSCOPE  STANDS,  BY  JOSEPH  ZENTMAYER,  147 
SOUTH  FOURTH  STREET,  PHILADELPHIA,  PA. 

American  Centennial  Stand,  binocular,  with  5  eye  pieces  $300  00 

Same,  but  monocular,  3  eye  pieces 250  00 

Concentric  adjustable  stage,  extra 20  00 

Best  mahogany  case,  with  fine  handle  and  side  case  —  30  00 
American  Histological  Stand,  with  plain  and  concave 
mirrors  attached  to  swinging  radial  bar,  carrying,  also, 
sub-stage  and  diaphragms  having  three  apertures,  1  (B) 

eye  piece,  no  case 30  00 

Extra  eye  pieces,  each 5  00 

NOTE.— The  following  extras  can  be  obtained  of  Mr. 
Zentmayer  at  the  prices  below  given.    They  are  fur- 


356  HOW    TO    SEE    WITH   THE   MICROSCOPE. 

nished  at  the  suggestion  of  the  author,  who  invariably 
orders  them  for  his  friends  and  pupils.  The  instru- 
ment is  thus  rendered  efficient  for  all  the  ordinary  pur- 
poses of  the  working  microscopist : 

Supplemental  revolving  stage $1  00 

Sub-stage  adapter,  to  carry  condenser,  society  screw 1  00 

Eye-piece  adapters,  ready  to  carry  solid  cells,  each 1  00 

8TAC4E  MICROMETERS,   TEST  PLATES,  ETC.,  BY  W. 
A.  ROGERS,  CAMBRIDGE  MASS. 

Mr.  Rogers  has  just  completed  his  new  machine,  in  the  con- 
struction of  which  several  important  improvements  have  been 
secured.  We  cheerfully  add  our  endorsement  as  to  the  regu- 
larity and  delicacy  of  his  rulings.  One  of  his  plates,  ruled  up  to 
120,000  lines  to  the  inch,  now  in  our  possession,  is  a  marvel  of  art. 
Owing  to  the  extreme  shallowness  of  Mr.  Rogers'  finer  rulings, 
they  are  more  difficult  tests  than  similar  bands  by  Nobert.  Mr. 
Rogers  furnishes  a  great  variety  of  work.  Some  of  his  regular 
plates  may  be  thus  described : 

Stage  Micrometer,  consisting  of  10  lines,  100,  and  10 
lines,  1,000  to  the  inch  $125 

Stage  Micrometer,  consisting  of  25  lines,  200  to  the  inch, 
10  lines,  1,000, 10  lines,  2,000,  10  lines,  4,000, 10  lines, 
5,000, 10  lines,  10,000, 10  lines,  20,000,  and  10  lines,  30,000 
to  the  inch 4  00 

Stage  Micrometers,  ruled  1,000, 10,000,20,000, 30,000, 40,000 
and  50,000  to  the  inch 500 

Same  as  above,  to  60,000 600 

»  "        to  70 ,000,  $7.00;  to  80,000,  $8.CO;  to  90,000        900 

^  "        to  100,000 1000 

(Closer  rulings  by  special  contract.) 

Standard  half-inches,  with  50  subdivisions  of  l-100th  inch 
and  10  subdivisions  in  the  centre  of  l-100th  inch :  3  00 

Standard  centimeters,  with  100  subdivisions 4  00 

(At  double  the  above  prices  Mr.  Rogers  furnishes  a 
complete  discussion  of  the  errors  of  the  plates,  and  a 


APPENDIX.  357 

table  showing  the  corrections  to  be  applied  to  each 
ruled  space  to  reduce  it  to  the  United  States  standard.) 

Standard  half  metres  and  standard   metres,  either  on 

glass,  steel,  iron  or  nickel  surface,  from  $25.00  to 100  00 

Test  plates,  micrometers,  etc.,  are  also  ruled  by  Mr.  Charles 
Fasoldt,  594  Broadway,  Troy,  N.Y.  The  author  has  one  of  Mr 
Fasoldt's  120,000  band  plates,  which  he  values  very  highly.  He 
regrets  not  being  able  to  give  Mrr  Fasoldt's  Catalogue  of  Prices. 


SUPPLEMENT. 


CONTRIBUTIONS  TO  THE  CINCINNATI  MEDICAL  NEWS. 

Inasmuch  as  the  author's  contributions  during  the  past  six 
years  to  the  pages  of  the  Cincinnati  Medical  News,  and  also  the 
American  Journal  of  Microscopy  contain  instructions  more  or 
less  interesting  to  those  commencing  the  study  of  the  micro- 
scope, it  is  thought  desirable  to  present  them  in  this  supplement. 
It  was  however  found  on  inquiry  that  the  back  numbers  ot  the 
Cincinnati  journal  were  not  to  be  obtained. 

Dr.  Blackham,  of  Dunkirk,  N.  Y..  kindly  placed  his  bound 
volumes  of  the  News  in  the  hands  of  the  writer,  thus  enabling 
him  to  give  the  reader  the  following  references,  dates,  etc.,  to 
the  several  articles  contained  in  the  Medical  News. 

1875.  January,  "  Microscope   Objectives,"   p.  41 ;     February 

"  Measurements  of  Moller  Probbe  Plate,"  p.  92;  March 
"Wide  us.  Low  Angled  Objectives,"  p.  129.;  April; 
"Diagnosis  of  Blood  Stains,  Dr.  Woodward  vs.  Dr! 
Richardson,"  p.  177.;  April,  "  A  Simple  Method  of 
Demonstrating  Aug.  Aperture,"  p.  1-83.;  May,  u  Wide 
vs.  Low  Angled  Objectives,"  p.  228.;  June,  "  Dr.  Ches- 
ter Morris'  Reports  on  Objectives,"  p.  281.;  November, 
"  Wide  vs.  Low  Angled  Objectives,"  p.  515. 

1876.  January, kl  Battle  of  the  Object-Glasses,"  p.  41.;  Febru- 

ary, "  The  Mic.  and  Its  Mis-iriterpretataions,"  p.  86.; 
March,  "  A  New  Microscope  Stage,"  p.  232.;  April, 
"Nobert's  19th  Band,"  p.  287.;  July,  "  Wythe's  Ampli- 
fiers," p.  433.;  August,  "  Prof.  J.  E.  Smith  us.  the 
Nachet  l-5th,"  p.  485.;  August,  "  Trichiniasis,"  p.  488. 
October,  "  Necessary  Manipulation  of  the  Microscope; 
to  Exhibit  Fine  Striae,"  p.  533.;  December,  "  Torula 
Cerevisse  in  Human  Urine,"  p.  677. 

358 


SUPPLEMENT.  359 

1877.    January,  "  Wenham's  Reflex  Illuminator,"  p.  74.;  July, 

"  R.  Hitchcock,  Esq.,  vs.  High  Angles,"  p.  504. 
The  past  contributions  to  the  American  Journal  of  Microscopy 
will,  owing  to  the  kindness  of  Prof.  Phin  be  given  in  full. 

PROF.  B.  HITCHCOCK   VS.   HIGH  ANGLES. 

In  the  May  number  of  the  American  Journal  of  Microscopy , 
I  find  an  article  containing  a  good-natured  criticism  of  a  paper 
read  by  me  before  the  Dunkirk  Microscopical  Society  last 
October. 

Mr.  Hitchcock  candidly  states  that  he  has  only  seen  a  short  - 
abstract  of  this  paper,  and  has  but  an  imperfect  knowledge  of 
it.    He  further  suggests  that  his  main  object  was  to  call  further 
attention  to  my  views,  and  he  suggests  that  I  put  them  in  form, 
so  as  to  be  published  iu  the  American  Journal. 

For  the  benefit  of  Mr.  Hitchcock,  I  will  state,  that  my  views 
have  been  clearly  stated  in  a  series  of  articles,  which  have  been 
published  in  the  Cincinnati  Medical  News  during  the  past  three 
years,  under  the  caption  of  "  High  us.  Low  Angles,"  and  have 
thence  been  quoted  from  and  reprinted  in  various  publications  ; 
certainly  I  cannot  be  expected  to  go  over  the  ground  anew  at 
this  late  day.  It  is  true  that  I  exhibited  before  the  Dunkirk 
Microscopical  Society  the  No.  20  of  the  balsam  Moller  probe 
platte,  and  also  the  19th  Nobert  band,  both  so  plainly  that  all 
who  were  present  saw  without  difficulty.  These  tests  were  not 
difficult  for  the  glasses  employed,  as  was  attested  by  the  fact 
that  they  were  shown  in  a  crowded  room,  amid  the  attendant 
jars  and  vibrations,  my  object  being  to  demonstrate  the  facility 
with  which  my  Tolles'  duplex  glasses  handled  these  so-called 
difficult  tests. 

To  show  the  work  of  these  same  lenses  by  central  light,  I 
selected  the  same  test.Nav.  Angulatum  which  the  biological 
committee  at  Philadelphia  has  declared  impossible  to  be  shown 
at  a  less  angle  than  20  degrees  from  axis,  with  any  medium 
power  glass.  This  test  was  displayed  illuminated  by  light 
through  a  central  aperture  placed  close  to  the  object,  just  large 
enough  to  light  the  field,  the  diameter  of  the  aperture  being 


360  HOW   TO    SEE    WITH   THE   MICROSCOPE. 

about  1-200  of  an  inch,  direct  light  being  used,  i.  e.,  without 
mirror  or  condenser.  The  ease  with  which  the  duplex  handled 
this  test  was  made  amusing  and  apparent  by  my  picking  up  the 
stand,  walking  around  the  room,  sitting  it  down  again  hap- 
hazard before  the  lamp,  when  the  resolution  was  found  by  a 
gentleman  appointed  to  examine  to  be  unimpaired.  This  was 
repeated  three  times.  Will  Mr.  Hitchcock  repeat,  using  a  low 
angle  glass,  be  it  a  one-fifth  or  a  one-fiftieth,  and  report? 

I  had  other  tests  for  central  light  work,  including  histological 
and  pathological  preparations.  It  was  impossible  to  show  all 
of  these  to  so  many  people  as  were  present,  as  it  was,  the  entire 
evening  after  the  readingjof  my  paper  was  occupied.  Hence,  it 
will  be  seen  that  I  fought  the  low  angles  on  their  own  chosen 
ground,  and  with  the  express  view  of  demonstrating  that  the 
very  best  preformance  of  the  duplex  lenses  is  seen  by  central 
light, 

Mr.  Hitchcock  further  says  that  "  the  universal  testimony  of 
our  best  authorities,  who  have  spent  their  lives  in  microscopical 
work,  is  against  Prof  Smith." 

It  was  just  this  kind  of  testimony  that  affirmed  a  few  years  ago, 
ths  highest  possible  aperture  of  an  object  glass  to  be  135  degrees; 
that  the  resolution  of  the  Nobert  19th  band  was  a  matter  of 
faith  rather  than  of  sight,  etc.,  etc.  Mr.  Hitchcock  is  welcome 
to  the  witnesses. 

Note  this  fact,  to- wit,  in  original  investigations,  the  advanced 
worker  must  necessarily  be  in  a  minority.  I  rejoice  that  some  of 
Mr.  Hitchcock's  witnesses  have  lately  found  cause  to  change 
their  opinions.  Dr.  Carpenter  will  no  longer  assert  that  the 
resolutions  of  the  Nobert  19th  band  is  a  k'  matter  of  faith,  rather 
than  of  sight."  On  the  other  hand,  he  has  given  unqualified 
endorsement  to  the  superiority  of  the  duplex  glasses. 

Mr.  Hitchcock  desires  to  ask  iohy  I  think  that  most  of  the  work 
in  histology  and  pathology  already"  done"  with  the  so-called 
"  working  lenses"  of  narrow  angles  would  require  further  atten- 
tion, and  with  wide  angled  glasses  I  reply,  that  in  the  past  four 
years  great  advances  have  been  made  in  the  construction  of 
objectives,  and  in  the  manipulation  of  the  microscope ;  what 
was  considered  a  "  good  working  glass"  ten  years  ago,  would 


SUPPLEMENT.  361 

mow  be  totally  valueless  for  advanced  work.  We  now  demand, 
as  near  as  may  be,  perfect  lenses,  and  superior  dexterity  in 
handling  them ;  and  these  two  conditions  are  inseparable.  The 
finer  the  objective  the  louder  the  call  for  expert  manipulations. 
That  well-known  term,  "  working  lenses  of  narrow  angles" 
means,  when  stripped  stark  naked,  easy  going  lenses,  with  no 
screw  collar  to  bother ;  good  working  lenses,  that  a  child  or 
sleepy  adult  without  experience  can  use  right  along,  will  work 
through  covers  of  common  window  glass,  big  working  distance, 
and  all  that,  etc.,  etc.  Such  are  admirably  adapted  to  the  use  of 
those  who  use  the  microscope  as  a  plaything  ;  admirable  things, 
too,  to  prove  that  "  a  little  knowledge  is  a  dangerous  thing." 

Be  it  known,  that  I  do  not  condemn  an  objective  simply 
because  it  has  a  narrow  aperture  ;  conversely,  I  do  not  endorse 
a  glass  on  account  of  its  wide  angle.  I  have  seen  scores  of 
wide  angle  glasses  not  worth  the  cost  of  their  brass  mountings. 
As  to  "errors  in  interpretation,"  the  more  perfect  the  lens,  and 
the  more  expert  the  manipulator,  the  less  chance  of  error. 
Under  high  amplifications,  a  superior  wide-angled  glass,  properly 
handled,  will  generally  prove  the  more  reliable  ;  and  in  advanced 
work  cannot  be  dispensed  with,  be  the  illumination  central  or 
oblique. 

Finally,  I  have  to  thank  Mr.  Hitchcock  for  his  friendly  criti- 
cism. He  seems,  evidently,  to  be  after  the  facts.  I  have  re- 
sponded to  his  request  as  well  as  I  could  with  my  limited  time 
and  space.  Two  hours  "over  the  tube"  would  demonstrate 
more  than  volumes  of  print. 

J.  EDWARDS  SMITH. 

Note. — On  my  last  visit  to  the  Dunkirk  Society,  May,  1877, 1 
showed,  I  believe,  for  the  first  time,  the  Nobert  19th  band  as  an 
vpaqvx  object,  with  my  Tolles'  one-tenth  duplex,  Beck's  vertical 
illuminator  being  used.  It  is  obvious  that  the  pencils  of  light 
traversing  that  band  were  at  least  centrally  disposed.  J.  E.  S. 

ANGULAli   APERTURE    AND    CENTRAL  ILLUMINATION. 

In  my  reply  to  Prof.  E.  Hitchcock,  reprinted  in  the  August 
number  of  this  journal,  I  endeavored  to  respond  to  his  court- 


362  HOW   TO    SEE   WITH   THE    MICROSCOPE. 

eous  request.  My  position  had  been  placed  fairly  before  the 
public  for  years,  and  I  was.  for  the  nonce,  content  in  maintain- 
ing silence,  feeling  assured  that  when  attention  should  be 
thoroughly  aroused  as  to  the  claims  of  high-angled  glasses,  that 
I  would  be  better  understood.  I  think  I  can  to-day  safely 
assert  that  my  expectations  have  been  realized,  and  to  a  greater 
extent  than  I  had  any  reason  to  anticipate. 

Prof.  Hitchcock  has  done  me  the  honor  of  an  extended  reply 
in  the  September  number  of  this  journal.  It  is  noticeable  that 
he  still  preserves  the  same  courteous  bearing  which  character- 
ized his  previous  paper ;  indeed  he  pays  me  a  compliment  ("We 
have  his  plain  statements,  and  we  accept,"  etc.,  p.  110).  All 
this,  as  an  index  of  his  good  nature,  is  very  acceptable. 

Nevertheless,  be  it  remembered  that  it  has  been  no  part  of  mv 
purpose  to  obtain  acceptance  per  se  of  my  positions.  On  the 
contrary  it  has  been  my  earnest  endeavor  to  excite  attention,. 
and  to  induce  my  readers  to  experiment  for  themselves.  Hence 
the  results  of  my  tedious  and  protracted  experience  with  the 
duplex  lenses  were  printed  in  forcible  terms  (heterodox  as  they 
must  have  seemed  to  many),  allowing  no  loop-hole  for  retraction 
or  qualification  on  my  part.  Hence  it  was,  too,  that  I  requested 
Prof.  Hitchcock  to  repeat  some  of  my  experiments ;  Prof.  II. 
is  compelled  to  decline,  because  he  has  not  the  objectives  at 
command.  This  I  sincerely  regret. 

Premising  that  my  time  is  fully  occupied,  and  that  it  will  be 
impossible  to  reply  directly  to  Piof.  Hitchcock's  last,  and  inter- 
esting paper,  I  proceed  to  offer  a  few  thoughts  suggested  by  -ne 
same. 

First,  what,  in  common  parlance,  constitutes  a  high-angled 
objective  ?  I  think  I  understand  Prof.  Hitchcock— perhaps 
not— let  us  see.  It  may  be  that  in  arriving  at  a  mutual  under- 
standing on  this  point,  we  may  get,  generally,  nearer  coinci- 
dence. Now,  most  observers  associate  with  the  term  "  high- 
angled  objectives,"  some  great  display  of  figures.  Thus,  175°r 
178°,  or  the  "  impossible  "  180°.  Others  might  go  still  further, 
turning  the  180°  corner,  and  thus  revel  in  the"  balsam  angles* 
say,  up  to  100°  or  higher.  Such  are  not  exactly  my  own  notions. 

I  regard  as  high-angled,  all  objectives   from  a  4-inch  to  a 


SUPPLEMENT.  363 

l-75th,  having  respectively  the  highest  possible  attainable  aper- 
ture. If  this  definition  be  accepted,  then  it  occurs  that  what 
was  known  as  a  high-angled  l-10th  of  130°  ten  years  ago,  would 
now  be  classed  as  a  medium-angled  glass,  and  further,  that  au 
inch  objective  of  45°  would  take  rank  as  a  high-angled  glass, 
and  to  the  latter  class  of  objectives  do  I  refer  as  giving  me  the 
best  results  for  any  and  all  work,  selecting  from  this  class  of 
objectives  the  one  best  adapted  for  the  work  in  hand.  Let  me 
illustrate  by  selecting  a  case  that  I  almost  daily  have  in  practice 
— to- wit : 

Suppose,  for  instance,  I  am  making  preparations,  »say,  of 
malignant  growths  (notice  that  this  is  not  a  diatom),  it  would 
doubtless  be  desirable  tirst  to  make  a  preliminary  examination. 
I  should,  from  the  high-angled  class  of  objectives,  select  the 
above  named  inch  of  45°.  Why  ? 

First,  because  it  has  large  working  distance,  which  is  not 
disturbed  by  high  eye-piecing.  I  am  also  enabled  to  bring  the 
mirror  above  the  stage,  and  thus  easily  condense  light  on  the 
object ;  and  further,  the  working  distance  is  so  large  that  little 
changes  in  the  same  do  not  disturb  the  object  to  such  an  object- 
ionable extent  as  would  occur  had  a  higher  power  been  selected. 

Second,  because  this  inch  will  show  me  structure  up  to  30,- 
000  lines  to  the  inch.  It  will  not  only  bear  the  l-4th  solid  eye- 
piece, but  will  give  with  it  added  force  of  definition,  with 
increased  amplification. 

Third,  (result  of  first  and  second),  because  of  all  glasses  I 
have  ever  handled,  I  can  get  the  most  work  (I  have  in  hnnd) 
out  of  it.  For  instance,  its  large  reach,  due  to  its  working  dis- 
tance (the  so-called  penetration),  enables  me  to  focus  through 
the  different  planes  of  the  object,  while  the  entire  specimen 
remains  fairly  in  view.  I  am  further  enabled  to  search  through 
my  mount,  with  the  least  danger  of  allowing  important  struc- 
tural elements  to  escape  my  attention— an  important  item. 

.N"ow,  should  such  preliminary  examination  suggest  the  pres- 
ence of  structure  calling  for  an  objective  capable  of  recognizing 
lines  100,000  to  the  inch  ;  the  inch  of  45°  would  be  removed,  and 
a  l-6th,  having  the  widest  aperture  known,  and  working  dis- 
tance of  one-fiftieth  of  an  inch,  substituted.  With  this  supe- 


3(34  HOW  TO    SEE   WITH   THE   MICROSCOPE. 

rior  defining  glass  I  have  still  working  distance  enough  to 
illuminate  my  object  by  condensing  sunlight  on  top  of  the 
cover,  thus  securing  exquisite  definition  under  amplification  of 
more  than  5,000  diameters.  Here,  again,  with  said  l-6th,  I  get 
better  work  than  I  can  with  any  other  style  of  glass. 

Again,  should  it  be  desirable  to  cross-question  my  specimen 
still  closer,  it  would  become  necessary  to  remove  the  l-6th  and 
substitute  a  bran-new  l-10th  not  yet  a  month  old,  the  master- 
piece of  a  young  American  optician.  This  l-10th  has  also  the 
widest  aperture  known,  combining  still  more  exquisite  defini- 
tion w^th  sufficient  working  distance  to  allow  the  use  of  sun- 
light as  above  named,  while  its  glorious  performances  by  central 
light  eclipse,  yea,  distance  the  work  of  any  low-angled  glass 
•extant,  this  beyond  the  ghost  of  a  doubt.  (And  right  here  I 
beg  Prof.  Hitchcock  to  be  lenient,  and  to  allow  me  a  little  mar- 
gin ;  it's  hard  to  keep  cool  over  the  central-light  performance  of 
this  new  MOth).  But,  with  the  employment  of  this  l-10th,  we 
get  into  tolerably  close  quarters,  the  "  difficulty  of  working  "  is 
enhanced.  It  won't  do  to  put  the  screw-collar  somewhere 
between  "  zero  "  and  somewhere  else.  And  then,  too,  there  has 
got  to  be  a  good  deal  of  that  ik  handling  "  attended  to  that 
Prof.  H.  says  will  do  so  well  to  talk  about  before  an  audience. 
Prof.  Hitchcock  here  applies  the  great  American  question,  and 
asks  if  all  this  bother  will  pay.  I  reply,  u  Yea,  verily  I" 

I  shall  be  very  grateful  if  Prof.  Hitchcock  will  point  me  to 
glasses  that  will  take  the  place  of  those  above  mentioned.  It 
has  so  happened  that  those  who  have  thus  far  undertaken  this 
task  (and  some  have  traveled  hundreds  of  miles  to  accomplish 
it)  have  resigned  their  previous  ideas  in  my  favor.  In  fact,  I 
have  scores  of  friends  made  in  just  this  kind  of  a  way,  and  I 
hope  to  add  Prof.  H.  to  the  list. 

Having  thus  given  my  ideas  as  to  the  nature  and  performance 
of  high-angled  objectives,  I  beg  to  add  that  I  see  no  necessity 
for  backing  down  from  my  original  statements,  although  chal- 
lenged by  Prof.  H.  On  the  contrary,  the  advent  of  the  new  l-10th 
serves  to  clinch  the  nail  that  I  had  previously  well-driven  home 
with  the  duplex.  And  I  now  place  again  on  record  my  deep- 


SUPPLEMENT.  365 

seated  convictions  that  the  use  of  such  lenses  as  I  have  de- 
scribed will  be  of  the  greatest  use  in  histological  observations. 

Prof.  Hitchcock's  remarkable  statement  that  •'  much  of  the 
very  best  class  of  work  is  being  done  with  second-class  lenses,'* 
is,  J  fear,  a  slip  of  the  pen.  I,  for  one,  certainly  cannot  agree 
with  him,  even  if  so  be,  that  I  am  found  in  a  u  minority.'7 

Prof.  Hitchcock  has,  I  fear,  found  out  my  weak  side,  and 
punches  me  sorely  with  Helmholtz's  formulas.  He  has  got 
things  nicely  tabulated,  to  show  at  a  glance  just  what  can  be 
done  and  what  can't.  Now,  I  own  up  that  of  all  the  annoying 
things  on  this  mundane  sphere  (to  me),  these  confounded  tables 
take  the  lead.  Years  after  others  as  well  as  myself,  saw  the 
19th  Nobert  band  as  clearly  as  we  saw  anything,  came  the 
tables  to  prove  that  the  thing  was  an  utter  impossibility  I 
It  was  noticeable  too  that,  year  after  year,  the  tables  got 
changed,  in  fact,  improved,  to  approximate  more  closely  to  the 
facts.  Verb.  sap. 

Again,  Mr.  Hitchcock  informs  us  that  "  to  attain  the  best 
possible  results  from  an  objective,  the  angle  of  the  illuminating- 
pencil  must  be  the  same  as  the  angular  aperture  of  the  objec- 
tive." This,  he  says,  is  the  "  chosen  ground  "  for  any  lens. 

To  put  it  mildly,  this  is  another  most  remarkable  statement. 
I  dismiss  it  with  the  remark  that  my  own  experience  teaches 
me  that  such  manipulation  would  defeat  ninety  low  angled 
glasses  out  of  the  hundred.  He  also,  referring  to  my  exhibition 
of  the  19th  Nobert  band,  with  the  vertical  illuminator,  sug- 
gests the  employment  of  a  diaphragm  to  the  back  lens,  pre- 
dicting that  the  resolution  would  "  doubtless  be  greatly 
improved."  I  had  already  tried  the  experiment  (and  scores  of 
others);  the  result  was  nil. 

Prof.  Hitchcock  further  says  that  "  Prof.  Smith  has  not 
taught  us  anything  new  about  objectives."  Well,  doubtless  a 
little  setting  back  of  this  kind  will  be  of  benefit  to  me,  and 
may  prevent  the  growth  of  undue  conceit.  I  confess,  that  I 
really  did  entertain  the  notion  that  some  of  my  "  shows  "  before 
the  Dunkirk  Microscopical  Society  were  novel.  For  instance, 
the  exhibition  of  the  Nobert  19th  band  as  an  opaque  object ; 
ditto,  the  showing  of  30,000  lines  to  the  inch  with  an  inch 
objective,  and  under  an  amplification  of  740  diameters,  etc. 


366  HOW   TO    SEE    WITH   THE    MICROSCOPE. 

It  was  my  intention  to  pass  over  one  or  two  points  presented 
by  Prof.  Hitchcock,  but  fearing  that  silence  may  be  miscon- 
strued, a  word  or  two  may  not  be  amiss.  Prof.  Hitchcock  does 
not  deny  that  Dr.  Carpenter  has  lately  (note  that  point)  given 
his  unqualified  endorsement  to  the  superiority  of  the  duplex 
glasses,  but  he  adds,  "  so  does  everybody  else."  This,  too,  must 
be  another  slip  of  the  pen,  for  it  is  all,  yea,  more  than  I  have 
claimed,  for  at  the  date  of  my  Dunkirk  lecture,  the  claims  of 
the  duplex  were  not  admitted  by  everybody.  During  the  past 
four  years  I  have,  myself,  received  hundreds  of  letters  from  as 
many  sceptics. 

Prof.  Hitchcock  states  that  he  was  taken  "a  little  by  surprise" 
by  my  claim  that  the  "  very  best  work  of  the  duplex  is  seen  by 
central  light,"  and  with  singular  tact  allows  the  little  fact  to 
remain  intact.  This  is  too  bad,  for  right  here  I  expected  the 
thickest  of  the  fight.  It  was,  in  fact,  "  my  chosen  ground." 
Prof.  H.  is  too  much  for  me  on  tactics. 

In  this  connection,  I  beg  the  reader  to  bear  in  mind  that 
while  Prof.  II.  admitted  the  superiority  of  wide  angles  for  the 
resolution  of  "  diatoms  and  Robert's  test-plates,"  he  neverthe- 
less held  that  this  did  not  support  my  view  that  high  angles  are 
"  universally  preferable,"  (see  this  journal,  May,  1877).  To 
meet  this  point,  I  stated  in  my  response  (this  journal,  August, 
1877,)  that  I  had  not  omitted  such  tests  as  are  generally  consid- 
ered "  chosen  ground  "  for  small  apertures,  i.  e.,  what  is  gener- 
ally understood  and  accepted  as  dead  central  illumination  ;  and 
further,  that  among  other  tests  I  selected  Navicula  angulata 
illuminated  by  central  light,  because  such  resolution  had  been 
publicly  declared  impossible.  In  reply  Prof.  II.  kindly  admits, 
and  in  complimentary  terms,  all  that  I  had  claimed  as  to  cen- 
tral light  work,  and  he  frankly  adds,  "  they  are  just  what  we 
would  naturally  expect  a  priori."  Having  made  this  full  admis- 
sion, Prof.  H.  seems  to  repent  a  little,  and  reverts  to  the  sub- 
ject again  (page  112),  still  yielding  that  the  high  angles  are 
superior,  both  with  oblique  or  central  illumination,  but  for  reso- 
lutions only,  because  he  says,  the  low  angles  have  the  greater 
penetration.  The  nature  of  this,  his  residual  error,  is  mani- 
festly indicated  in  the  piesent  paper.  Less  than  IV  Uvo  hours 


SUPPLEMENT.  367 

over  the  tube  "  would  convince  Prof.  Hitchcock  that  u  the  very 
best  performance  (penetration,  depth  of  focus,  reach,  or  what 
not  included)  is  seen  by  central  light.  I  again  invite  investi- 
gation. The  passage  from  Frey  was  original  with  Dr.  Carpen- 
ter ten  years  ago.  I  have  no  objection  to  urge. 

A  word,  and  let  it  bo  with  due  respect  to  Dr.  Carpenter.  His 
advanced  age  and  failing  eyesight,  together  with  his  many 
duties  and  cares,  forbid  that  he  should  continue  to  be  the 
authority  he  has  been  in  the  past.  Singularly  enough,  the 
doctrines  advanced  by  Dr.  Carpenter  twelve  years  ago  are  still 
endorsed  by  many  to-day.  This  operates  as  a  brake  to  the 
wheel  of  progress ;  surely  Dr.  C.  is  not  to  blame.  Mr.  Hitch- 
cock asks  if  Dr.  C.  has  changed  his  opinion  since  the  fifth  edi- 
tion of  his  work  ;  in  reply,  I  can  say  that  the  latest  information 
I  have  bearing  on  this  point  is  this;  about  eighteen  months 
since  a  friend  of  mine  was  in  London  attending  medical  lect- 
ures. He  sought  Dr.  Carpenter's  advice  as  to  objectives ;  Dr. 
C.  advised  him  to  go  home  and  purchase  the  duplex,  and  my 
friend  did  so  purchase.  Be  all  this  as  it  may,  while  I  enter- 
tain the  highest  respect  and  admiration  for  his  medical  and 
scientific  attainments— his  life  of  unceasing  toil  in  his  profes- 
sion—I cannot,  and  for  the  reasons  presented,  attach  impor- 
tance to  Dr.  Carpenter's  endorsement  of  the  duplex  glasses. 
In  other  words,  I  should  prefer  the  testimony  of  American 
experts. 

To  resume,  Mr.  Hitchcock  further  says  that  "  two  hours  over 
the  tube  "  has  demonstrated  something,  he  don't  say  exactly 
what.  At  anyrate  he  volunteers  his  thanks,  which  I  joyfully 
accept.  I  should  have  said  that  "  two  hours  jointly  over  the 
tube  "  would  demonstrate  more  than  volumes  of  print.  1  hope 
yet  to  enjoy  such  a  tete-a-tete  with  friend  Hitchcock,  and  prom- 
ise in  advance  to  delight  him  with  the  new  wide-angled  l-10th 
before  referred  to.  The  new  glass,  too,  confirms  in  a  truly 
practical  manner  the  positions  I  have  heretofore  taken  in  print. 

In  conclusion,  I  have  again  to  thank  Prof.  Hitchcock  for  his 
good  natured  review  of  my  previous  article,  and  hope  that  he 
will  find  nothing  in  this  hastily  written  article  objectionable. 


368  HOW   TO    SEE    WITH   THE    MICROSCOPE. 


A  FEW    WORDS  CONGE  LINING    THE   PERFORMANCE  OF     OBJEC- 
TIVES. 

Ed.  Am.  Jour.  Microscopy— Referring  to  the  letters  of  Mr.  E. 
Gundlach,  printed  in  the  August  issue  of  the  Cincinnati  Medi- 
cal News,  it  was  noticed  that  Mr.  Gundlach  bases  his  optical 
laws  on  the  performance  of  his  own  objectives,  or  at  least  he 
appeals  confidently  to  his  objectives  to  sustain  his  positions,  as 
to  working  distance,  resolution  and  angular  aperture. 

Mr.  Gundlach  certainly  has  the  right  to  state  the  principles 
which  govern  him  in  the  construction  of  object-glasses,  and  it 
would  be  well  if  other  makers  would  follow  his  example.  But 
his  readers  must  keep  constantly  in  mind  that  while  the  general 
principles  he  sets  forth  may  not,  as  a  rule,  differ  materially  from 
those  actuating  other  opticans,  each  and  every  one  has  a 
handling  characteristically  his  own,  and  that  a  necessary  result 
of  his  will  be  recognized  in  the  characteristic  performance  of 
various  so-called  first-class  objectives ;  and  further,  that  between 
the  extremes  comprised  in  the  "  handling"  above  named,  a  large 
margin  obtains,  sufficient  to  warrant  the  acceptance  of  one  ob- 
jective to  the  exclusion  of  another. 

The  potency  of  these  considerations  is  enhanced  when  we 
remember  that  the  slightest  superiority  in  an  objective  is  of  the 
highest  importance.  Beale  says  ("How  to  Work  with  the 
Microscope,"  p.  285)  "It  is  certain  that  the  slightest  advantage 
iii  defining  power  ought  not  to  be  underrated.  *  *  *  Im- 
provement in  the  means  of  observation  is  of  the  utmost  im- 
portance, and  however  slight,  always  leads  to  the  discovery  of 
new  facts." 

Again  Dr.  Beale  writes  (p.  283)  -l  The  best  object-glasses  will 
define  clearly  and  accurately  bodies  which,  from  their  trans- 
parency, are  quite  invisible  under  objectives  only  slightly  in- 
ferior to  the  first." 

It  therefore  becomes  apparent  that  these  little  differences, 
perhaps  due  to  "  handling"  on  the  part  of  the  optician,  while 
they  are  invaluable  to  the  working  microscopist,  may  also  be 
referable  to  the  genius  of  the  optician— to  a  particular  method 
of  "handling"  known  optical  laws. 


SUPPLEMENT.  369 

By  way  of  illustrating  these  "little  differences,"  it  may  be 
mentioned  that  among  first- class  objectives  of  the  same  mag- 
nification, aperture  and  resolving  power,  greater  and  lesser 
working  distance  will  be  found,  and  right  here  is  the  solution 
of  the  dogma  of  (bo-called)  penetration,  for,  of  the  glasses  above 
mentioned,  that  one  having  the  greater  working  distance  will 
be  endowed  with  the  greater  penetration.  This  is  the  whole 
thing  in  a  nutshell,  as  set  forth  by  the  writer  years  ago. 

If,  in  the  comparison  of  two  objectives,  alike  in  magnification, 
aperture  and  resolving  power,  one  shall  be  found  to  have  the 
longer  working  distance,  then  is  its  superiority  demonstrated, 
and,  be  it  remembered,  that  comparisons  of  objectives  ought 
always  to  be  made  in  this  kind  of  a  way,  otherwise  any  attempt 
at  comparison  would  be  as  futile  as  if  we  were  to  compare  a  tur- 
nip with  an  orange. 

Again,  ij  it  can  be  shown  that  a  medium  power  glass,  say  a 
l-6th  or  a  1-lOth  having  the  widest  aperture  known,  and  also  com- 
paratively large  working  distance,  say  l-50th  of  an  inch,  will 
more  than  do  any  work  that  can  be  done  with  objectives  of  ex- 
ceedingly high  power,  and  correspondingly  short  working  dis- 
tance [excess  of  aperture  being  barred  by  the  above  named 
conditions),  it  will  be  obvious  that  the  former  will  be  eminently 
the  superior  glass. 

Now  the  facts  warrant  the  assertion  that  just  such  one-sixth 
and  one-tenth  are  made,  and  by  American  opticians.  The 
writer  has  had,  and  still  has  in  his  possession  just  such  glasses. 
His  first  contribution  to  the  columns  of  the  News,  four  years 
since,  set  forth  their  claims,  and  he  has  never  had  occasion  to 
make  either  modification  or  retraction  of  his  original  statement. 
When  such  occasion  shall  occur,  the  readers,  of  this  journal  will 
be  promptly  advised ;  until  then  I  claim  (especially  for  the  one- 
sixth)  unequaled  intensity  of  definition,  widest  known  aperture, 
combined  with  large  working  distance— in  other  words,  without 
that  sacrifice  of  "  working  distance"  alluded  to  by  Mr. 
Gundlach. 

I  embrace  this,  my  first  opportunity,  to  say  that  I  have  lately 
examined  at  length  a  new  duplex  one-tenth,  the  work  of  a 
young  American  optician.  This  new  one-tenth  is  similar  in 

24  Microscopy. 


370  HOW   TO    SEE    WITH   THE    MICROSCOPE. 

aperture  and  has  greater  working  distance  than  my  own  one- 
tenth  ;  its  work  over  such  tests  as  the  Nobert  and  Moller  (balsam) 
plates  was  quite  equal  to  that  of  its  formidable  competitor, 
while  the  views  it  gave  by  central  light  were  simply  glorious, 
excelling  the  old  one-tenth.  This,  as  a  first  attempt  on  the  part 
of  a  young  optician,  is  truly  encouraging.  These  new  duplex 
glasses  will  receive  my  earnest  attention,  and  I  may  have,  in  the 
future,  something  more  to  say  about  them. 

Allow  me  to  further  state,  that,  being  desirous  of  acquainting 
myself  with  the  work  of  our  own  opticians,  I  wrote  to  the 
Rochester  firm,  asking  the  loan  of  objectives  for  examination 
and  study.  They  responded  promptly,  sending  me  by  return  mail 
a  full  line  of  Mr.  Gundlach's  lowest  priced  "  Student's"  work. 
They  certainly  had  no  time  to  select  exceptional  glasses.  My 
time  has  been  so  thoroughly  occupied,  I  have  not  yet  given  them 
the  attention  they  deserve,  but  as  far  as  they  have  been  examined 
J  am  much  pleased  with  them— a  three-fourth  inch  at  $6,  a  one- 
half  inch  at  $8,  and  a  three-tenths  at  $11 ,  are  very  finejindeed 
for  their  cost. 


ANGULAR  APERTURE  ONCE  MORE. 

Ed.  Am.  Jour.  Microscopy.—  The  discussion  between  Prof. 
Hitchcock  and  myself,  which,  during  the  last  few  months  you 
have  done  us  the  honor  to  print,  seems  to  have  become  some- 
what of  a  rambling  nature.  Prof.  Hitchcock  "  changes  base  " 
so  often,  that  it  would  bother  a  streak  of  lightning  to  catch  — 
much  less  corner  him.  Be  this  as  it  may — and  perchance  he 
might  return  the  compliment,  1  can  only  say  that  I  have  endeav- 
ored to  stick  to  the  points  at  issue— the  merits  of  high,  as  com- 
pared with  low  angles,  I  have  attempted  to  set  forth  from  a 
practical  standpoint,  being  tolerably  familiar  with  the  use  of 
either  style  of  glass. 

I  have  tried  my  best  to  have  Prof.  Hitchcock  examine  high- 
angled  glasses  for  himself,  and  report  results,  but,  as  your  read- 
ers are  aware,  from  his  own  assertions,  Prof.  Hitchcock  does 
not  claim  a  practical  knowledge  of  them,  and  as  a  matter  of 
course  he  cannot  see  what  that  "  handling  "  (of  which  it  will  do 


SUPPLEMENT. 


371 


so  well  "  to  talk  about  before  an  audience  ")  amounts  to.  Of  a 
piece  with  this  comes  his  statements  that  such  and  such  posi- 
tions of  my  own  are  **  not  proved,"  and  that  before  he  accepts 
them  he  "  must  know  why." 

I  submit :  that  the  only  possible  method  of  convincing  Prof. 
Hitchcock  will  be  the  practical  one,  in  this  instance,  however, 
quite  impracticable,  to-wit :  "  two  (or  more)  hours  conjointly 
over  the  tube,"  or  until  he  shall  have  done  me  the  honor  to 
adopt  my  suggestion,  and  experiment  with  the  high  angles  for 
himself ;  in  the  latter  case,  obviously,  he  ought  not  to  expect 
nrst-class  results  from  the  wide  angles  until  at  least  he  shall 
have  learned  that  something  is  due  to  "  handling."  I  repeat 
that  until  one  or  the  other  expedient  is  adopted,  we  might  con- 
tinue the  present  discussion  until  doomsday,  and  on  my  part 
without  a  vistige  of  any  chance  of  convincing  Prof.  Hitchcock. 
I  therefore  offer  the  following  brief  remarks  by  way  of  closing 
a  controversy  which,  in  the  nature  of  things  cannot  lead  to  any 
fixed  results. 

Prof.  Hitchcock  asks,  "  Why  strain  a  one-inch  to  see  30,000 
lines  to  an  inch,  with  a  deep  eye-piece,  when  the  half-inch 
would  do  the  same  work  without  being  pressed  so  hard  ?" 

Well,  let  us  strip  things  "  stark  naked,"  and  find  out  tk  why." 
First,  with  the  inch  I  get  better  definition ;  second,  longer 
working  distance  ;  and,  third,  because  the  inch,  with  deep  eye- 
piecing  "  is  not  pressed  so  hard  as  the  half-inch— and  this  is 
my  reply  to  Prof.  Hitchcock.  As  a  matter  of  course  he  will 
come  back  at  me  with  the  stereotyped  assertion,  "  I  must  know 
why."  He  says,  too,  u  Until  his  (my)  experiments  are  published 
and  subiected  to  public  examination  they  are  not  to  be  accept- 
ed, etc."  Well,  by  the  laws,  my  experiments  have  been  both 
published  and  subjected  to  public  examination.  But,  unfortu- 
nately, Prof.  H.  wasn't  there  !  Note  that. 

Further,  I  now  propose  to  put  the  inch  and  half-inch  to  a 
practical  test.  Thus,  let  Prof.  Bodgers,  of  Cambridge,  rule  a 
band  of  40,000  lines  to  the  inch,  and  let  Prof.  Hitchcock  count 
them  if  he  can  with  a  low  half-inch  (say  of  40°).  I  hazard  the 
prediction  that  he  will  fail,  and  furthermore,  that  I  will  be 
enabled  to  count  them  with  an  inch  of  45°.  I  am  ready  for  such 
test  in  any  shape  that  Prof.  Hitchcock  may  suggest. 


372  HOW   TO    SEE    WITH   THE   MICROSCOPE. 

To  get  back  to  our  "  moutons."  When  I  stated  30,000  as  the 
limit  for  definition  of  the  inch,  I  held  a  good  large  margin  (to 
swear  by)  in  reserve.  This,  as  the  30,000  was  "  millions  "  as  far 
as  establishing  my  point  was  concerned,  now  that  the  readers  of 
this  journal  have  got  used  to  the  •'  30  "  I  will  add  that  I  have  no 
trouble  in  seeing  the  40,000  band  of  a  Rodger's  test-plate,  and 
most  beautifully  ruled  they  are.  Here  is  an  added  strain  of  ten 
thousand  on  the  inch,  but  it  is  as  good  as  ever !  (One  of  these 
days  I  must  give  your  readers  a  description  of  an  exquisitely 
ruled  plate,  up  to  80,000  to  the  inch,  an.d  by  the  same  talented 
artist.) 

But  to  business.  I  have  as  fine  a  half-inch  of  38°  as  I  have 
ever  seen,  a  glass  selected  with  much  care,  having  spent  consid- 
erable time  in  making  the  selection,  so  as  to  have  the  very  best; 
for,  be  it  known,  I  sometimes  (not  often)  have  use  for  just  this 
sort  of  glass.  Well,  now,  this  half-inch  has  shorter  working 
distance,  and,  as  a  matter  of  course,  less  penetration  than  has 
the  inch  of  45°,  while  the  last-named  inch  of  45°  has  much  the 
superior  definition. 

Now,  I  am  perfectly  acquainted  with  the  u  points  "  of  these 
two  objectives,  and  can  make  either  put  its  '"  best  foot  fore- 
most," (hence  the  "  handling  "  may  be  counted  out.)  Both  are 
my  own,  and  I  can  at  will  use  ths  one  that  I  prefer.  Which 
would  Prof.  Hitchcock  use  under  tbe  same  circumstances  ?  Or, 
leaving  the  Professor  out,  which  would  the  reader  select  ? 
Which  glass  would  be  "  strained  "  the  most  ? 

Prof.  Hitchcock  reminds  his  readers  that  he  has  "  already  ad- 
mitted to  Prof.  Smith  that  Tolles  and  Spencer  are  making  won- 
derful glasses,  etc."  Yes,  so  he  did,  but  he  put  a  fence  round 
them  ;  thus  he  adds  "  but  for  resolutions  only."  When  Prof. 
Hitchcock  shall  become  as  well  acquainted  with  the  work  of 
Spencer  and  Tolles  as  are  others,  that  fence  will  step  down  and 
out.  I  accept  no  loop-hole,  but  stand  to  the  position  heretofore 
assumed,  to-wit,  that  the  above  named  glasses  are  not  equalled 
for  kt  any  and  all  work,"  a«  set  forth  in  my  last  paper. 

Now  about  Dr.  Johnson's  showing  the  19th  band  as  an  opaque 
object  in  the  year  1872  or  thereabouts.  Here  is  a  legitimate 
chance  to  try  on  Pro'f.  Hitchcock's  conditions,  to-wit:  Were 


SUPPLEMENT.  373 

Dr.  Johnson's  experiments  with  the  19th  band  published  ?  (as 
were  my  own).  Again,  were  they  "  subjected  "  to  public  exam- 
ination ?"  (as  were -my  own.)  Let  the  Professor's  rule 
work  both  ways.  Meanwhile  I  no*v  assert,  and  know 
whereof  I  affirm,  that  a  Powell  &  Lealand  l-10th  of  1872 
cannot  be  forced  to  show  the  19th  band  by  lamplight.  In  gen- 
eral, I  don't  propose  to  accept  anything  done  with  the  19th  band 
live  years  ago,  as  comparable  with  what  is  being  done  in  1877. 
Again,  all  who  have  seen  the  19th  band  as  displayed  with  the 
duplex  and  modified  Beck  illuminator,  instantly  admit  that  for 
wondrous  delicacy  of  definition,  the  total  absence  of  the  "ghost" 
of  a  diffraction  line,  all  other  methods  of  illumination  (by  arti- 
ficial light)  are  simply  "  nowhere."  And  further,  that  any 
attempt  at  photographing  these  wonderful  lines  has  been  but 
approximative.  To  be  more  definite,  the  best  photograph  of  the 
19th  band  yet  made  is  simply  a  caricature.  Nevertheless  it  is 
wonderful  that  Col.  Woodward  has  succeeded  as  well  as  he  has, 
and  his  photographs  are  the  best  that  I  have  seen. 

A  word  as  to  the  mathematical  tables.  There  can  be  no  pos- 
sible objection  to  these,  when  (it's  my  chance  to  say  "  when  " 
now)  they  agree  with  obvious  facts ;  they  are  objectionable  when 
they  are  not  in  accord  with  facts.  I  stand  ready  to  accept  truth 
in  any  form  ;  ditto,  to  repel  error.  Now  the  facts  are,  that  from 
a  mathematical  standpoint  the  limits  of  vision  have  been 
erroneously  "  set "  again  and  again.  I  simply  protest  against 
fighting  facts  with  mathematics— simply  this,  and  nothing  more. 

In  drawing  towards  the  close  of  this  article,  I  desire,  as  apro- 
pos to  the  question  at  issue,  to  state  a  little  bit  of  personal  expe- 
rience, viz  :  About  a  year  ago  a  gentleman,  a  professor  occupy- 
ing a  responsible  position,  gave  me  a  carte  blanche  to  provide  him 
with  a  medium  power  lens.  He  was  particular  to  state  that  he 
was  engaged  in  histological  studies,  and  wanted  the  glass  for 
such  and  similar  purposes.  In  response,  he  was  furnished  with 
a  l-6th  duplex.  Last  summer  he  visited  me  during  his  vacation 
and  became  my  pupil.  He  was,  of  course,  an  apt  scholar,  and 
quick  to  learn.  He  spent  with  me  weeks  in  acquiring  the  man- 
ipulations of  this  glass,  and  became  quite  expert.  When  he  left 
me  he  said,  "  I  have  now  learned  practically  what  was  done  for 


374  HOW  TO   SEE   WITH   THE   MICROSCOPE. 

me  in  the  selection  of  the  objective,  which  I  now  prize  more 
than  ever,  and  it  is  astonishing  how  much  is  due  to  handling.  I 
had  no  idea  of  it."  A  few  weeks  ago  he  wrote  me  that  he  was 
doing  finely  with  the  duplex,  and  had  succeeded  with  it  in  trac- 
ing structure  (histological)  that  could  not  possibly  have  been 
seen  with  any  low-angled  glass.  Further,  that  the  very  best 
makes  of  the  low  angles  were  constantly  within  his  reach. 

Now  it  is  a  fact  that  before  I  furnished  this  gentleman  with 
the  duplex,  he  was  as  fully  committed  in  favor  of  low  angles  as 
Prof.  Hitchcock  can  be ;  but,  unlike  Prof.  H.,  he  commenced 
the  study  of  high  apertures,  and  with  the  sure  results  above 
narrated.  His  address  will  be  furnished  to  any  one  desiring  it. 

Prof.  Hitchcock  says  something  (I  quote  from  memory)  about 
"  accepting  defeat  in  a  becoming  manner."  I  desire  most  earn- 
estly to  advertise  the  fact  that  it  is  not,  has  not,  been  any  part 
of  my  purpose  to  u  defeat "  Prof.  Hitchcock,  and  as  I  have 
understood  the  gentleman  from  the  very  onset,  he  is  not,  nor 
has  he  been,  in  a  position  to  suffer  defeat.  He  simply  wants 
the  facts,  and  I  have  endeavored  to  furnish  them,  and  if  so  be 
that  any  good  has  been  brought  about  by  this  discussion,  your 
readers  are  quite  as  much  indebted  to  Prof.  Hitchcock  as  to  any 
one  else. 

In  conclusion,  I  return  Prof.  Hitchcock  my  sincere  thanks 
for  the  courteous  and  gentlemanly  consideration  he  has 
ever  extended  me.  It  has  been  my  intention  to  reciprocate,  and 
with  the  hope  that  I  have  been  in  a  measure  successfnl,  and 
with  the  kindest  feelings  towards  Prof.  Hitchcock,  to  you  Mr. 
Editor,  and  to  your  many  readers,  I  remain  sincerely  yours, 

J.  EDWARDS  SMITH. 

NOTE.— In  your  October  number,  page  132,  an  obvious  error 
occurs.  For  "  what  was  known  as  a  high-angled  l-10th  of  180° 
ten  years  ago,"  read  lk  130°  ten  years  ago,"  etc.  J.  E.  S. 


SUPPLEMENT.  375 


DISCURSORY  THOUGHTS    RELATING    TO    THE   USE  AND   ABUSE 
OF  THE   MICROSCOPE. 

An  Address   delivered  by  Prof.   J.  Edwards  Smith,    before  the  Dunkirk 
Microscopical  Society,  Tuesday  Evening,  October  31,  1876. 

To  the  Members  of  the  Dunkirk  Microscopical  Society  : 

GENTLEMEN:— About  twelve  months  ago  a  friend  of  mine  and 
a  brother  microscopist,  ordered  from  London  a  low-angled  l-4th 
inch  objective ;  my  friend  was  engaged  in  histological  investiga- 
tions, and  felt  the  need  of  a  reliable  medium-power  glass.  He 
had  been  told  that  wide-angled  glasses,  although  very  suitable 
for  the  purposes  of  the  diatomist,  were  hardly  suitable  for  the 
work  he  had  in  hand ;  he  was  told,  too,  that  the  thing  needed 
was  a  glass  of  low  or  moderate  angle,  say  from  50°  to  70°,  and 
one  that  had  great  working  distance ;  in  short,  as  the  saying 
goes,  he  needed  a  good  "  working  glass." 

In  due  time  the  objective  was  received,  and  one  very  pleasant 
evening  my  friend  called  on  me  expressly  to  show  the  work  of 
the  lens.  I  remember  that  we  had  a  very  enjoyable  time,  amus- 
ing ourselves  by  looking  over  a  variety  of  specimens  suitable 
for  the  glass.  In  the  course  of  the  evening  he  exhibited  a  beau- 
tiful section  of  a  human  tooth,  and  placing  the  same  under  the 
l-4th,  called  my  attention  to  the  "Nasmyth's  membrane," 
described  by  Frey  and  others. 

This  was  a  matter  of  interest  to  me,  for  I  had  heard  much  of 
this  "  Kasmyth's  membrane ;"  I  had  examined  human  teeth 
time  and  time  again  with  my  own  wide-angled  glasses,  but  had 
never  been  able  to  discover  the  same.  I  was,  in  fact,  somewhat 
curious  about  the  matter.  It  seemed  odd,  to  say  the  least,  that 
my  glasses,  which  would  show  me  clearly  and  accurately,  lines 
as  close  as  120,000  to  the  English  inch,  should  fail  to  show  me 
the  existence  of  a  membrane  said  to  be  about  1-6,000  of  an  inch 
in  thickness ;  and  then  again  I  had  hunted  with  a  low-angled 
l-4th  of  my  own  without  success.  Hence  it  was  with  expect- 
ancy and  interest  that  I  put  my  eye  to  the  tube  ;  I  saw  a 
decided  thickening  of  the  margin  of  the  crown  of  the  tooth,  and 
was  informed  that  this  was  the  veritable  "Nasmyth."  But, 


376  HOW   TO    SEE    WITH   THE   MICROSCOPE. 

said  I,  "  is  this  thickened  edge  not  the  fault  of  the  objective, 
and  suppose  that  we  examine  the  specimen  with  another  glass?" 

Removing  the  London  lens,  I  substituted  a  wide-angled  l-6th 
of  plus  180°  of  aperture,  and  on  adjusting  carefully  to  the  thick- 
ness of  covering  glass,  I  soon  had  a  splendid  view  of  the  pre- 
paration, by  far  finer  than  that  shown  by  the  London  glass ; 
and  as  I  had  supposed  would  be  the  case,  I  now  had  a  nice 
clean  edge  in  the  place  of  the  thickened  one  before  mentioned. 
The  superiority  of  the  definition  over  that  of  the  l-4th  was 
apparent;  and  tht  capacity  of  the  1 -6th  to  bear  the  1 -4th  inch 
solid  eye-piece  and  amplifier— thus  carrying  the  amplification 
up  to  nearly  4,000  diameters— was  in  a  few  moments  demonstra- 
ted, but  the  Nasmyth's  membrane  was  not  to  be  seen  uitder  any 
amplification. 

At  this  time  it  occurred  to  me  that  I  might  possibly  make  a 
membrane  as  described  by  the  books,  and  as  shown  by  the  Lon- 
don lens.  Turning  the  collar  of  the  l-6th  so  as  to  throw  the 
glass  considerably  out  of  adjustment,  and  again  focussing  the 
object,  I  was  much  amused  to  find  that  I  had  the  identical 
membrane,  as  shown  by  the  imported  glass,  and  also,  that  as 
tht  collar  was  moved,  the  membrane  could  be  made  thick  or 
thin  to  suit  I 

The  result  of  this  little  episode  was  simply  this — my  friend 
now  owns  and  uses  on  histological  work  an  American  made  l-6th 
of  180°  of  aperture. 

I  have  related,  as  briefly  as  possible,  this  little  incident,  and 
exactly  as  it  occurred.  I  desire  to  say,  however,  that  I  do  not 
deny  the  existence  of  "  Nasmyth's  membrane,"  described  in  the 
various  works  on  physiology  and  histology.  Nevertheless  can- 
dor compels  me  to  state  that  I  have  in  times  past  made  diligent 
search,  and  have  failed  to  recognize  a  structure  which  is  taught 
even  in  our  elementary  school  books,  as  if  it  were  a  common- 
place thing ! 

Months  ago  it  occurred  to  me  that  the  membrane  referred  to 
might  only  be  found  on  teeth  of  the  first  dentition,  and  obvi- 
ously would  be  found  wanting  on  the  tooth  of  an  adult.  This 
idea  sent  me  to  the  dentist's  office  :  such  specimens  were  pro- 
cured, but  the  u  Nasmyth  "  still  defeated  my  search  therefor. 


SUPPLEMENT.  377 

Some  months  ago  I  was  engaged  in  teaching  microscopy  in 
one  of  our  public  schools.  At  that  time  I  had  the  class  in 
physiology  in  hand,  and  it  was  my  especial  purpose  to  show 
them  actually,  structures  which  were  described  and  pictured  in 
the  text  book  used.  I  had  not  proceeded  far  before  we  ran 
against  this  "  Nasmyth's  membrane,"  and  I  was  compelled  to 
state  substantially  the  experience  which  I  have  now  related  to 
you. 

There  is  not  a  class  of  persons  on  earth  Jess  appreciated  or 
more  poorly  paid  than  those  engaged  in  histological  investiga- 
tions, and  for  their  indefatigable  perseverance  I  entertain  a 
profound  respect ;  but  it  has  often  occurred  to  me  that  as  a  class 
they  have  been  content  to  work  with  very  poor  tools,  and  it  is 
safe  to  say  that  a  great  deal  of  the  ground  already  studied  will 
have  to  be  reinvestigated,  and  with  better  glasses— with  a  bet- 
ter knowledge  of  those  manipulations  requisite  to  the  use  of 
wide-angled  lenses.  Nor  can  the  necessary  manipulations  be 
acquired  in  the  ordinary  routine  of  investigation  ;  it  is  an  art 
of  itself,  and  calls  for  special  attention,  requiring  as  much 
study  as  the  art  of  manipulating  a  pianoforte  or  an  organ. 

It  is  a  very  commonplace  remark,  that,  for  the  purposes  of  the 
histologist,  low-angled  glasses,  of  moderate  definition,  are  the 
best  suited.  And  yet,  if  we  consult  their  latest  works,  we  will 
find  structures  described  that  call  for  the  best  lenses  of  the 
widest  angles.  Take,  for  instance,  the  muscle  sheaths,  or  the 
axis  cylinders  of  the  nerves  described  by  Frey,  in  his  last 
edition.  Coming  down  to  commonplace  things,  I  affirm  that 
the  simple  trachea  of  a  bee  cannot  be  studied  with  advantage 
with  other  than  lenses  of  the  widest  angles. 

There  is  perhaps  no  microscopic  object  more  common  than 
these  tracheaes.  They  are  to  be  found  mounted  in  the  cabinet 
of  every  microscopist,  and  we  have  all  of  us  read  about  them 
in  the  books ;  we  have  examined  them  again  and  again,  times 
without  number,  with  objectives  ranging  from  the  inch  to 
the  l-5th,  or  perhaps  to  the  l-10th.  Now  I  ask  you  take  a  look 
at  them  on  my  account,  and  if  possible  inform  me  how  these 
tracheal  coils  terminate  :  what  is  the  structure  at  their  very  last 
end?  What  is  the  least  diameter  of  these  terminal  coils  V  Here 


378  HOW   TO   SEE   WITH   THE    MICROSCOPE. 

you  have  a  problem  in  hand,  to  which,  for  exquisite  intensity  of 
definition,  or  nicety  of  manipulation,  the  resolution  of  the 
Moller  or  Nobert  plates  are  child's-play  matters  !  And  if  you 
should  be  desirous  of  testing  your  lenses  as  to  their  capacity  for 
histological  work,  the  trachea  will  be  found  to  be  one  of  the 
very  best  test  objects  in  existence,  and  will  surely  furnish  you 
valuable  ideas  as  to  the  relative  value  of  wide  and  low  angled 
glasses  for  the  purposes  of  histological  research. 

Not  long  since  one  of  our  most  skilful  physicians  sent  me  a 
sample  of  urine  from  a  child  supposed  to  be  suffering  from  a 
disease  of  the  kidneys.  Jt  was  a  perplexing  case,  and  the  med- 
ical gentleman  in  charge  hoped  that  the  microscope  would  give 
some  light  on  the  case  ;  when  examined  with  a  low  power  l-5th 
of  70Q  aperture,  the  specimen  appeared  in  every  respect 
healthy  ;  but  on  further  examination  with  a  wide-angled  glass, 
and  with  an  amplification  of  nearly  4,000  diameters,  it  was- 
found  to  be  literally  swarming  with  vibriones.  There  were  bil- 
lions upon  billions  of  them  in  every  field  examined,  all  of  which 
were  totally  invisible  to  the  low-angled  l-5th. 

We  often  hear  the  remark,  that  wide -angled  glasses  are  just 
the  thing  for  the  display  of  lined  objects,  surface  markingsr 
diatoms,  etc.,  but  that  owing  to  their  short  focal  length,  and 
limited  working  distance — the  trouble  attending  the  adjustment 
of  collar — and  in  general,  the  difficulties  pertaining  to  their  user 
that  they  are  unsuited  to  the  purposes  of  the  histologist ;  white 
on  the  contrary,  low-angled  glasses  of  greater  working  distance 
requiring  no  skill  in  management,  are  the  tools  with  which  the 
real  work  of  the  microscope  has  been,  and  will  continue  to  be 
done,  and  such  are  fondly  termed  good,  honest  and  reliable 
"  working  glasses." 

1  can  never  listen  to  this  line  of  argument  without  entertain- 
ing the  suspicion  that  sloth  and  inactivity  lay  at  the  bottom.  We 
never  hear  astronomers  complain  of  the  care  they  are  compelled 
to  use  in  instrumentation ;  on  the  contrary,  they  pride  them- 
selves on  the  accomplishment  of  being  able  to  work  instruments- 
requiring  a  great  amount  of  skill  and  precision  in  manipula- 
tion. 
The  objection  of  short  working  distance  originated  years  ago» 


SUPPLEMENT.  379 

when  German  pathologists  were  in  the  habit  of  using  common 
window  glass  to  cover  their  mounts,  and  at  that  time  the 
extremely  thin  glass,  now  so  easily  obtainable,  was  unknown. 
All  this  is  now  changed  ;  the  widest  angled  lenses  known  giving 
all  desirable  amplification,  will  admit  the  use  of  covers  l-50th 
of  an  inch  thick,  while  covering  glass  measuring  .003  can  easily 
be  procured. 

A  vast  amount  of  work  has  been  done  with  these  kl  honest 
and  reliable  working  glasses,"  and,  as  I  have  before  said,  will 
have  to  be  done  over  again,  and  this  revisory  work  is  now  in 
progress.  But  while  there  is  some  excuse  for  the  investigators 
of  the  past,  who  used  the  best  instruments  then  obtainable,, 
what  shall  we  say  of  those  of  to-day  who  persistently  refuse  to 
avail  themselves  of  the  wonderful  progress  the  optician  is  able 
to  demonstrate  in  this  centennial  year  V 

I  have  advanced  the  idea  that  working  pathologists  were  too 
often  content  to  work  with  poor  tools.  1  made  that  remark  in- 
good  faith,  and  believe  tnat  it  will  be  found  to  be  trne.  Never- 
theless the  pathologists  of  the  past,  or  even  of  the  present  day,, 
are  by  no  means  wholly  at  fault,  when  we  remember  that  the 
entire  corps  .of  observers  to  whom  we  are  indebted  for  all  that 
has  been  taught  through  the  aid  of  the  microscope,  were  men 
who  were  regularly  engaged  in  the  respective  duties  of  their 
several  professions,  and  that  most  of  them  have  rilled  profes- 
sional chairs  in  various  institutions  of  learning.  These  men,  in 
studying  the  use  of  the  microscope,  each  and  every  one  of  them 
were  compelled  to  dig  and  trench  for  themselves; -the  instru- 
ment which  to  them  was  as  all-important  as  the  compass  to  the 
navigator,  was  far,  very  far,  from  being  as  true  and  reliable  as- 
kk  the  needle  to  the  pole."  Once  launched  on  the  unknown,  but 
to  them,  fascinating  sea  of  scientific  investigation,  every  spare 
moment  that  could  be  snatched  from  their  regular  engagements 
was  devoted  to  its  exploration.  It  was  a  tiny  sea,  within  a 
microcosm,  replete  with  interest,  and  capable,  as  if  by  the  touch 
of  the  optician's  wand,  of  boundless  expansion  ! 

These  self-abnegating,  self-sacrificing  men  fully  accomplished 
their  task.  It  was  a  labor  of  love,  and  the  results  they  obtained 
were  given  to  the  world  without  money  and  without  price. 


380  HOW   TO   SEE   WITH   THE   MICROSCOPE. 

Among  the  investigators  of  our  own  day,  1  will  refer  you  to 
one  whose  untiring  industry  has  earned  for  him  a  world-wide 
reputation.  I  allude  to  Dr.  Lionel  S.  Beale,  F.  E.  S.  Dr. 
Beale,  as  you  are  aware,  has  been  contemporary  with,  and  the 
supporter  of,  Dr.  Carpenter's  heretofore  universally  received 
opinions  as  to  the  relative  capacity  of  wide  and  low  angled 
objectives.  Dr.  Beale,  in  his  work,  "  How  to  Work  with  the 
Microscope,"—  I  quote  from  the  third  edition,  page  7  — says  as 
follows  :  "  For  ordinary  work  it  will  be  found  inconvenient  if 
the  object-glass  when  in  focus  comes  too  close  to  the  object. 
This  is  a  defect  in  glasses  having  a  high  angle  of  aperture.  *  * 
Glasses  with  a  high  angle  of  aperture  admit  much  light,  and 
define  many  structures  of  an  exceedingly  delicate  nature,  which 
look  confused  when  examined  by  ordinary  powers.  For  general 
work  I  recommend  glasses  with  an  angle  of  not  more  than  50Q 
to  1000 

lk  Mr.  Boss  has  lately  made  glasses  having  an  angle  of  170°, 
which  are  valuable  for  investigations  upon  very  delicate  and 
thin  structures,  such  as  the  diatomaceae ;  but  such  powers  are 
not  well  adapted  for  ordinary  work.  The  importance  of 
arranging  the  object  very  carefully,  and  the  necessity  of  paying 
.great  attention  to  the  illumination,  render  these  glasses  incon- 
venient for  general  observation.  The  penetrating  power  of 
.glasses  with  a  low  angle  is  much  greater  than  in  those  of  a  high 
angle  of  aperture,  so  that  exact  focussing  is  much  more  impor- 
tant in  the  latter  than  in  the  former." 

This,  in  its  popular  acceptation,  is  the  square  doctrine  first 
advanced  by  Dr.  Carpenter,  and  it  has  suffered  no  loss  by  its 
filtration  through  the  mind  of  Dr.  Beale.  It  is  the  doctrine 
which  has  been  generally  received  and  accepted.  It  is  the 
dogma  which  ten  years  ago  I  thought  ought  not  to  be  true,  and 
of  which  to-night  I  stand  before  you  the  prince  of  sceptics  I 

In  the  quotation  which  1  have  presented,  there  are  two  domi- 
nant ideas ;  the  one  displays  the  inconvenience  attending  the  use 
of  wide-angled  glasses,  and  to  this  objection  I  have  already 
paid  my  respests  in  due  form ;  the  other  presents  the  theory  of 
**  penetration  "  as  originally  advanced  by  Dr.  Carpenter,  sup- 


SUPPLEMENT.  381 

ported  by  Dr.  Beale,  and  generally  endorsed  by  microscopists 
of  Europe  and  America. 

I  have  not  the  time  this  evening,  nor  would  I  weary  your 
patience  by  the  discussion  of  this  dogma  of  penetration,  any 
further  than  to  admit  that  it  was  true  ten  years  ago,  when  first 
announced  by  Dr.  Carpenter,  but  can  .have  no  possible  present 
force  in  reference  to  the  wide  aperture  glasses  of  to-day.  I  am 
also  quite  prepared  to  grant  that  a  spectacle  lens  of  sixty  inches- 
focus  needs  less  skill  in  management  than  a  duplex  l-10th  of 
plus  180°  of  aperture ! 

After  all,  I  get  considerable  comfort  out  of  -the  quotation 
already  presented.  Dr.  Beale  says,  "  that  glasses  with  a  high 
angle  of  aperture  admit  much  light,  and  define  many  structures 
of  an  exceedingly  delicate  nature,  which  look  confused  when 
examined  by  ordinary  powers."  Notice  the  wording ;  he  does 
not  say  diatoms.  He  does  say,  u  many  structures  of  an  exceed- 
ingly delicate  nature,  which  look  confused  when  examined  by 
ordinary  powers."  It  is  a  candid  and  manly  admission,  and  E 
honor  his  candor.  It  is  the  truth,  the  whole  truth,  and  nothing 
but  the  truth  ;  while  for  brevity  of  form,  or  clearness  of  expres- 
sion, these  half  dozen  words  leave  nothing  to  be  desired  beyond 
what  is  here  so  forcibly  stated ;  and  I  bet?  of  you  not  to  lose 
sight  of  the  fact  that  if  this  was  true  of  wide- angled  glasses 
made  in  1865,  it  is  equally  so  of  those  of  1876. 

Another  fact  will  bear  to  be  borne  in  mind.  It  is  this  :  when 
Dr.  Beale  wrote  in  1865,  he  was  very  far  from  being  expert  in 
the  use  of  wide  apertures.  I  wiH  read  to  you  further  from  the 
same  paragraph :  "  In  order  to  adjust  the  object-glass,  it  is- 
first  arranged  for  an  uncovered  object ;  then  any  object  covered 
with  thin  glass  is  brought  into  focus  by  moving  the  body  of  the- 
microscope ;  next,  the  ring  which  carries  the  third  lens  is 
screwed  round  until  any  particles  of  dust  upon  the  upper  sur- 
face of  the  glass  are  brought  into  focus.  The  glass  is  then  cor- 
rected for  examining  the  covered  object  which  may  be  brought 
into  focus."  It  will  be  seen  that  the  method  of  adjustment 
adopted  by  Dr.  Beale  is  precisely  the  same  as  that  used  by 
many  for  measuring  the  thickness  of  covering  glass,  and  when 
the  milled  head  of  the  fine  adjustment  is  properly  graduated,  and 


382  HOW   TO    SEE    WITH   THE   MICROSCOPE. 

the  "  run"  of  the  fine  adjustment  is  known,  the  plan  is  a  con- 
venient one,  and  will  give  measures  tolerably  correct ;  but  for 
the  purpose  of  adjusting  an  object-glass  it  is  obviously  fanlty, 
and  would  in  almost  every  instance  defeat  such  wide  angled 
lenses  as  I  am  in  the  habit  of  using.  Dr.  Beale's  instructions 
MS  to  the  adjustment  of  wide-angled  lenses  must  be  taken  "cum 
grano  salis,"  aud  will  indeed  be  more  honored  in  the  breach 
than  in  the  observance. 

It  is  with  pleasure  that  I  now  turn  to  page  217,  and  read  as 
follows:  "Besides  extreme  minuteness  in  mere  size,  extreme 
tenuity  or  transparancy  may  interfere  with  the  definition  of  an 
object.  Now  the  greatest  difference  is  observed  in  object- 
glasses  in  this  particular.  The  best  object-glasses  will  define 
dearly  and  accurately— mark  the  words,"  clearly  and  accurately" 
—bodies  which,  from  their  transparency,  are  quite  invisible 
under  objectives  only  slightly  inferior  to  the  first." 

Now  the  question  arises  at  once,  Where  shall  we  find  these 
best  object-glasses,  which  define  so  clearly  and  so  accurately 
such  delicate  and  transparent  objects?  Referring  again  to 
page  7,  Dr.  Beale  responds  thus  :  "  Glasses  with  a  high  angle 
of  aperture  admit  much  light,  and  define  many  objects  of  an 
exceedingly  delicate  nature,  which  look  confused  when  exam- 
ined by  ordinary  powers." 

The  Doctor  having  thus  squarely  settled  the  question,  most 
kindly  goes  on  to  tell  us  where  we  can  get  these  wide-angled 
glasses,  and  I  read  right  along,  as  before  quoted :  "  Mr.  Ross 
has  lately  made  glasses  having  an  angle  of  170°,  which  are  valu- 
able for  investigations  upon  very  many  delicate  and  thin  struc- 
tures," etc.,  etc. 

It  is  especially  a  part  of  my  purpose  in  appearing  before  you 
this  evening  to  show  you  "  clearly  and  accurately,"  and  by  the 
aid  of  glasses  of  American  manufacture,  which  for  width  of 
aperture  have  never  been  excelled,  some  of  these  extremely  thin 
and  transparent  objects,  and  thus  prove  to  you  the  truth  of  Dr. 
Beale's  assertion ;  and  relying  on  the  correctness  of  the  old 
adage  that  "  seeing  is  believing,"  I  can  hardly  fail  in  the 
demonstration  of  the  accuracy  of  Dr.  Beale's  position. 

Pardon  a  momentary  digression,  and  allow  nie  to  turn  to  page 


SUPPLEMENT.  383 

216.  Here  I  read  :  u  If  any  one  makes  out  new  points  of  struc- 
ture by  any  new  method,  all  that  such  an  authority  who  differs 
has  to  do  is  to  state  that  he  has  not  been  able  to  see  the  struc- 
ture described  so  and  so.  Authority  too  often  denies  the  ex- 
istence of  what  it  has  itself  been  unable  to  see.  Many  auth- 
orities deny  the  existence  of  what  they  haye  not  seen,  while 
they  have  not  taken  the  pains  to  try  the  only  method  of  demon- 
stration by  which  the  appearances  in  question  could  be  seen." 

Now  we  perceive  that  the  Doctor  is  in  a  complaining  mood. 
The  root  of  the  matter  was  simply  this  :  Dr.  Beale  paid  great 
attention  to  instrumentation ;  the  first  l-25th  arid  the  first  l-50th 
objectives  in  existence  were  made  for  him  ;  he  was  not  very  par- 
ticular as  to  their  angle,  although  it  is  noticeable  that  he 
claimed  for  them  "  plenty  of  light."  But  the  fact  is  indisput- 
able that  his  instrumentation  has  been  in  advance  of  that  of  the 
London  microscopists.  Dr.  Beale  was  in  fact  in  a  position  very 
similar  to  those  of  the  present  day,  who,  conscious  of  the  superi- 
ority of  their  glasses,  are  disposed  to  regard  the  blind  "  authori- 
ties "  referred  to  as  unworthy  of  special  consideration. 

I  desire  in  this  connection  to  call  your  attention  to  the  history 
of  the  diatom  of  which  we  have  all  of  us  heard  so  much  about 
during  the  past  nine  years.  I  refer  to  Amphipleura  pellucida. 
Who  of  us  here  cannot  recall  the  time  when  the  existence  of 
striae  on  this  shell  was  stoutly  denied  V  We  can  remember,  too, 
when  Dr.  Woodward  settled  this  much  vexed  question  by  pro- 
ducing his  photographs  displaying  the  striae  on  what  he  was 
pleased  to  call  "  this  well-marked  diatom."  And  now  that  these 
markings  are  no  longer  to  be  questioned,  as  exhibited  on  dry 
mounts,  and  by  the  employment  of  monochromatic  sunlight, 
full  eighty  per  cent,  of  our  American  observers  fail  to  exhibit 
41  this  well-marked  diatom"  by  lamp  illumination,  even  when 
dry  mounted.  I  have  a  balsam  mount  of  this  shell  with  me, 
and  hope  to  show  you  the  lines  of  No.  20  of  the  Holier  plate 
this  eyening  before  we  part,  and  also  the  19th  band  of  the 
Nobert  test  plate,  and  by  the  aid  of  American  made  lenses  of 
medium  power. 

Let  me  call  your  attention,  for  a  few  moments  only,  to  another 
subject.  We  often  hear  the  diatomist  spoken  of  in  terms, 


384  HOW   TO    SEE   WITH  THE    MICROSCOPE. 

almost,  of  contempt.  They  are  too  often  regarded  by  the  hist- 
ologist  as  a  class  of  observers  who  use  the  microscope  as  a  mere 
plaything ;  and  the  fact  that  the  diatomists  are  not  altogether 
agreed  as  to  the  structure  of  some  of  their  favorite  shells,  is. 
often  used  as  an  argument  to  show  the  folly  of  studying  the 
diatomacese  at  all  ! 

All  'this,  my  friends,  is  sheer  sophistry.  The  study  of  the  dia- 
tomacese  is  as  legitimate  as  that  of  any  other  branch  of  the 
science  of  biology,  and  the  labors  of  the  diatomists  have  not 
been  for  naught ;  it  is  to  them,  and  to  their  constant  demands 
on  the  optician,  that  we  are  indebted  for  the  wonderful 
improvements  which  have  been  made  in  object-glasses;  and  I  am 
bold  enough  to  tell  you  that  skillful  diatomists  can  tell  you  a» 
much  concerning  the  structure  of  a  diatom,  as  can  the  patholo- 
gist—equally skilled— inform  you  as  to  the  structure  of  a  blood 
corpuscle  ! 

But  to  the  student,  to  those  who  desire  to  prepare  themselves 
for  advanced  work,  the  study  of  the  diatomaceae  cannot  be  neg- 
lected. No  line  of  practice  has  yet  been  discovered  that  will 
teach  the  student  the  use  and  management  of  his  tools,  that 
can  at  all  compete  with  the  superior  claims  of  these  minute 'org- 
anisms. It  is  said  that  "  adversity  tries  us  and  shows  up  our 
best  qualities."  These  little  shells,  too,  will  try  the  would-be- 
manipulator,  and,  like  the  country  judge,  show  up  his  worst 
qualities. 

It  was  not  my  purpose  to  enter  at  all  into  the  details  concern- 
ing the  use  of  objectives ;  but  it  will  perhaps  be  well  not  to  let 
the  opportunity  pass  without  alluding  to  the  fact  that  a  wide- 
angled  glass  requires  totally  different  management,  in  some 
respects,  from  those  of  narrow  apertures. 

Those  who  have  been  accustomed  to  the  use  of  the  low  angles 
will,  on  a  slight  acquaintance  with  glasses  possessing  wide  aper- 
tures, almost  invariably  assert  that  the  latter  do  not  give  as 
good  results,  when  worked  by  central,  of  centrally  disposed 
light,  as  they  are  accustomed  to  get  from  the  former.  A 
moment  or  two  devoted  to  the  consideration  of  the  situation, 
will,  I  think,  furnish  the  key  thereto. 

When  we  use  a  narrow-angled  objective,  the  oblique  or  lateral 


SUPPLEMENT.  385 

rays  are  per  force  excluded.  The  objective  will  not  receive 
them,  and  there  can  be  no  possible  doubt  but  that  such  work  is 
being  done  with  centrally  disposed  light,  such  as  the  observer 
desires ;  there  is  no  special  manipulation  or  management  neces- 
sary to  secure  this,  for  the  objective  will  admit  centrally  dis- 
posed rays,  and  none  other. 

But  in  the  handling  of  a  wide-angled  lens  the  conditions  are 
essentially  changed,  and  this  change  of  condition  involves  in 
turn  a  change  of  handling,  and  of  management. 

Hence  it  occurs,  that  in  using  a  wide-angled  glass  by  central 
or  centrally  disposed  light,  some  arrangement  must  be  provided 
for  the  purpose  of  shutting  out  the  lateral  rays ;  these  the  glass 
will  admit,  and  in  default  of  the  provision  referred  to,  will  steal 
in,  cause  interference,  and  defeat  both  observer  and  objective. 
To  shut  out  these  lateral  pencils  would  seem  eminently  the  bus- 
iness of  the  usual  diaphragm  box. 

This  provoking  little  piece  of  apparatus,  this  diaphragm  box, 
is  supplied  with  almost  every  stand  in  use,  and  is  as  faulty  in 
operation  as  human  ingenuity  in  construction  could  devise  ;  in 
general  these  boxes  are  furnished  with  a  shutter  pierced  with 
openings  of  various  sizes,  and  placed  from  one-half  to  one  inch 
below  the  object-carrier  of  the  stage.  Now,  suppose  we  are 
using  a  wide-angled  lens,  and  being  desirous  of  central  light 
only,  we  attempt  the  use  of  the  smallest  opening  of  the  shutter. 
What  now  is  the  result  ? 

It  is  as  follows :  the  pencils  of  light  enter  the  small  aperture, 
emerge  and  diverge  within,  and  fill  the  box  with  simply  light  of 
low  intensity.  It  has  now  become  a  washed-out,  wire-drawn 
light,  lacking  force,  and,  I  may  say,  velocity ;  the  objective  now 
in  turn  receives  this  much- abused  illumination,  not  only  the 
central  pencils  thereof,  but  lateral  ones  also ;  and  the  working 
angle  used  will  be  determined  by  the  depth  and  diameter  of  the 
diaphragm  box. 

A  proper  diaphragm  for  general  use— not  diaphragm  box,  for 
the  less  of  the  box  the  better — is  a  plate  pierced  with  a  central 
opening  of  about  the  size  of  a  large  needle,  and  so  mounted  as 
to  approach  the  iower  edge  of  the  mount  closely  as  possible 
without  suffering  actual  contact.  To  construct  this  little  piece 

25  Microscopy. 


386  HOW  TO   SEE   WITH   THE   MICROSCOPE. 

of  apparatus  will  not  make  any  very  severe  demands  on  your 
mechanical  skill. 

Those  of  my  hearers  who  read  the  London  Monthly  Micro- 
scopical Journal  will  remember  that  the  capacity  to  display  the 
markings  of  Navicula  angulata  by  central  light,  was  considered 
a  feat  only  to  be  performed  by  low-angled  glasses  of  superior 
excellence.  Some  of  you,  too,  may  have  read  the  report  of  a 
certain  biological  committee  who  met  in  Philadelphia  last  year 
for  the  purpose  of  testing  the  object  glasses  of  several  makers  ; 
one  of  the  tests  used  was  the  exhibition  of  the  markings  of  this 
same  dry  mounted  Navicula  angulata  by  central  light. 

I  was  simply  astounded  when  I  read  the  report,  in  public 
print,  of  this  biological  committee,  and  learned  that  in  their 
hands  that  Angulata  had  defeated  a  wide-angled  American 
l-10th,  and  I  immediately  repeated  the  experiment,  using  a 
similar  l-10th,  by  the  same  maker,  and  worked  with  a  dia- 
phragm plate  perforated  with  an  opening,  say,  l-200th  of  an  inch 
in  diameter,  and  placed  almost  in  contact  with  the  under  sur- 
face of  the  mount.  The  result  was  amusing  enough  !  I  instantly 
had  the  markings  "  clearly  and  accurately  "  defined  ;  the  prob- 
lem was,  indeed,  to  avoid  seeing  them  I  In  fact  nothing  short 
of  sheer  intention,  or,  what  is  worse,  bad  manipulation,  could 
have  defeated  the  objective.  I  then  repeated  the  experiment, 
using  this  time  a  balsam  mounted  Angulata— the  !No.  11  of  the 
Moller  plate — and  was  almost  instantly  rewarded,  as  in  the  pre- 
vious instance.  I  am  prepared  to  again  repeat  this  experiment 
this  evening  should  you  so  desire. 

Again,  the  converse  of  what  has  been  said  is  also  true,  namely 
in  working  with  a  wide-angled  objective,  and  with.oblique  light, 
it  is  important  to  shut  out  the  central  pencils.  About  a  year 
ago,  I  devised  a  simple  little  instrument,  which  gave  access  only 
to  a  narrow  wedge  of  oblique  light,  and  thus  gave  added  force 
to  the  definition  of  the  objective— and  this  "oblique  dia- 
phragm "  was  permanently  fitted  to  the  stage  of  my  stand. 

The  most  efficient  instrument  of  this  nature,  however,  is 
"Wenham's  reflex  illuminator,"  an  ingenious  accessory,  and  so 
contrived  as  to  shut  out  all  rays  less  than  41°  interior,  which,  of 
course,  has  emergence  at  90°  into  air.  The  reflex  illuminator, 


SUPPLEMENT.  387 

which  was  designed  by  its  inventor  to  give  a  dark  field, 
becomes,  when  used  on  balsam  mounts,  with  American  object- 
glasses,  having  balsam  angles  ranging  in  the  nineties,  not  a 
reflex,  but  a  direct  illuminator,  and  a  most  efficient  aid  to  the 
definition  of  the  lens.  By  it  I  am  enabled  to  show  the  trans- 
verse striae  of  Ko.  20  of  the  Holier  plate  so  clearly  that  any  old 
lady  who  can  read  her  family  bible  could  hardly  fail  of  recog- 
nizing the  striae  on  "this  well-marked  diatom."  I  have  the 
instrument  with  me,  and  shall  be  happy  to  show  you  its  work 
on  the  Moller  plate.  * 

It  was  mainly  the  purpose  of  these  desultory  remarks  to  call 
your  attention  to  the  importance  of  instrumentation  ;  absolute 
perfection  has  not  been,  and  never  will  be  obtained.  There 
never  has  been,  nor  will  there  ever  be  made,  an  instrument  of 
precision  that  does  not  embody  inherently  some  radical  weak- 
ness, some  dangerous  fault.  The  practical  astronomer  is  not 
only  early  taught  the  nature  and  use  of  the  various  instruments 
to  be  found  in  the  observatory,  and  made  acquainted  with  their 
several  imperfections,  both  optical  and  mechanical,  but  he  is 
compelled  to  acquaint  himself  thoroughly  with  the  methods 
employed  to  eliminate  these  imperfections.  Having  thus  per- 
force of  his  preliminary  study  acquired  a  thorough  perception 
of  the  Scylla  and  Oharybdis  which  environ  the  use  of  instru- 
ments, it  becomes  in  turn  a  life's  study  to  further  remove  exist- 
ing difficulties,  or  to  provide  better  and  more  competent  means 
of  compensation  therefor. 

I  have  no  doubt  but  that  it  would  be  interesting  and  instruc- 
tive to  detail  some  of  .the  exquisitely  precise  methods  employed 
by  the  astronomer  to  detect  and  compensate  for  the  unavoidable 
errors  of  instrumentation,  but  time  forbids.  I  will,  however, 

*  immediately  after  the  introduction  of  the  "  reflex,"  mod. neat  ions,  by 
changing-  the  angle  cf  the  facet,  were  made  by  the  London  opticians,  so  as 
to  adapt  the  instrument  to  their  variously-angled  objectives,  similar  modi- 
fications were  also  made  here  in  this  country,  by  Messrs.  Tolles  &  Spencer. 
Three  years  ago  the  writer  consulted  a  skilled  artist  with  the  view  of  mak- 
ing-the  "  reflex"  in  three  separate  mountings,  changing  the  angle  of  the 
facet  in  each.  Nevertheless,  the  idea  is  Weuham's.  The  mere  matter  of 
changing  the  angle  of  the  facet  would  naturally  occur  to  any  one  using  the 
instrument— J.  E.  S.  January,  1878. 


388  HOW   TO    SEE    WITH   THE    MICROSCOPE. 

notice  th«  nature  of  one  or  two  difficulties  which  may  be  said  to 
infest  the  observatory. 

We  are  all  familiar  with  the  purpose  for  which  the  transit 
instrument  is  employed,  namely,  to  observe  the  transit  of  celes- 
tial bodies  across  the  meridian  in  which  the  transit  is  adjusted. 
To  accomplish  this,  it  is  evident  that  the  instrument  must  be 
permanently  placed  in  that  meridian ;  bnt,  unfortunately,  the 
block  of  stone  has  yet  to  be  found  solid  enough  for  the  purpose. 
Hence  it  is  usual  to  ascertain  the  direction  and  amount  of  error 
and  thus  correct  the  results  obtained  by  observing  with  the 
instrument  while  out  of  the  plane  of  the  meridian.  The  alti- 
tude and  azimuth  instrument,  too,  requires  frequent  and  careful 
attention.  To  be  assured  that  its  object-glass  may  swing  in  a 
vertical  plane,  observations  are  nightly  made  by  observing  a 
distant  star  directly,  and  immediately  afterwards  its  image  as 
seen  in  the  mercurial  horizon.  By  this  means  a  truly  vertical 
line  millions  of  miles  in  length  is  obtained. 

Reflecting  instruments  constructed  on  the  model  of  the  sex- 
tant, are  cross-questioned  by  observations  on  east  and  west 
stars,  and  errors  due  to  eccentricity  thereby  avoided. 

Not  only  do  these  painstaking  men  study  their  instruments, 
but  they  in  like  manner  study  themselves,  and  their  capacity  to 
observe  is  cross-questioned  in  the  severest  manner.  It  is  to 
them  well  known  that  the  observations  of  some  first-class 
observers  are  constantly  affected  with  a  plus  sign ;  while,  again, 
those  of  other  equally  good  observers  are  affected  in  a  contrary 
direction.  This  individual  condition  is  called  "  personal  equa- 
ion,"  and  has  to  be  thoroughly  known  and  compensated  for; 
and  this  you.  must  bear  in  mind,  that  the  amount  of  error  due  to 
personal  equation  is  always  comparatively  small,  and  as  a  con- 
sequence is  only  recognized  in  the  observations  of  professional 
experts,  trained  to  machine-like,  impassive  regularity. 

My  initial  remarks,  in  which  the  kt  Nasmyth's  "  membrane  of 
the  books  was  discussed  in  a  somewhat  discursory  manner,  were 
intended  as  an  example,  and  to  give  you  an  illustration  in  refer- 
ence to  a  radical  evil,  which  has  in  times  past  tainted  the  obser- 
vations of  many  who  use  the  microscope— I  refer  to  diffraction 
lines  and  diffraction  borders.  To  avoid  these  spectral,  illusory 


SUPPLEMENT.  389 

appearances,  is  a  consideration  of  the  very  first  importance- 
requiring,  too,  the  employment  of  the  finest  object-glasses,  and 
that  technical  skill  in  the  adjustment  thereof,  which  is  only 
acquired  by  long  practice ;  and  to  this  end  the  study  of  the  dia- 
t^macese  will  be  found  in  the  highest  Degree  advantageous. 
Moreover,  one  must  devote  a  good  deal  of  study  to  this  ghostly 
parasite,  which  t:oo  often  infests,  and  to  a  greater  or  less  extent 
defeats  the  unsuspecting  observer.  And  here  again  the  little 
diatom  will  render  yeoman's  service. 

Some  months  ago,  Dr.  Woodward,  to  whom  we  are  all  so 
much  indebted  published  in  the  London  Monthly  Microscopical 
Journal,  for  the  express  purpose  of  displaying  these  illusory  ap- 
pearances, a  lithograph  from  his  photograph  of  Frmlulia,  Sax- 
onica.  The  objective  used  by  Dr.  Woodward  was  an  American 
l-18th,  and  was  the  same  glass  with  which  his  inimitable  photo- 
graphs of  the  19th  Kobert  band  were  accomplished. 

I  took  it  for  granted  that  the  lithograph  of  Fmstulia  Saxonica 
was  made  with  the  glass  intentionally  placed  out  of  adjustment, 
and  for  the  purpose  of  creating  these  particular  lines.  A  copy 
of  the  London  journal  is  placed  at  our  service  this  evening,  and 
I  invite  your  inspection  of  the  plate  referred  to.  The  whole 
shell  of  the  diatom  will  be  seen  badly  distorted,  the  striae  badly 
denned,  and  the  diffraction  lines  are  immense  I"  * 

*I  may  here  remark  that  only  a  few  hours  ago  my  attention  was  called  to 
a  report  of  a  meeting:  of  the  London  Microscopical  Society,  held  April  5, 
1876,  and  t  eported  in  the  May  number  of  the  London  Microscopical  Journal. 

Alluding:  to  the  photographs  of  Frustulia  Saxonica,  Mr.  John  Mayall  said: 
"  Kvery  one  who  is  familiar  with  the  Frustul'a  Saxonica,  photographs  of 
which  Dr.  Woodward  sent  in  illustration  of  his  paper  in  December,  knows 
it  to  be  one  of  the  most  difficult  test-objects  — a  diatom  that  ranks  next  to 
Amphipleura  pellucida.  That  particular  form  of  Frustulia  is  one  that  I 
have  rare  y  seen  resolved,  except  by  lenses  of  the  highest  excellence.  I 
consider  Dr.  Woodward's  photographs  of  it  as  in  every  way  most  remark- 
able, evincing  first-rate  skill  brought  to  bear  on  one  of  the  finest  known 
lenses."  It  is  hard  to  tell  which  is  the  most  "remarkaole,"  the  photographs, 
or  this  statement  of  Mr.  Mayall's. 

As  there  seems  to  be  much  difference  of  opinion  as  to  these  representa- 
tions of  Frustulia  Saxonica,  both  at  h  »me  and  abroad,  a  word  or  two  may  be 
admissable.  When  the  lithographs  first  made  their  appearance  in  the  Lon- 
don Monthly  MicroscopiealJournal^  one  of  our  most  talented  experts  wrote 


390  HOW  TO   SEE   WITH  THE   MICROSCOPE. 

Now,  after  seeing  and  learning  what  can  be  accomplished 
with  a  superior  objective,  when  out  of  adjustment,  it  will  be 
instructive,  and  I  shall  beg  your  permission,  by  the  employ- 
ment of  a  superb  glass,  accurately  adjusted,  to  show  you  a  sim- 
ilar, but  more  difficult  tiaxonica,  as  illuminated  by  the  most 
oblique  beams  my  extremely  thin  stage  will  admit.  Thus  han- 
dled the  resolution  of  JFrustulia  Saxonica  becomes  one  of  the 
most  charming  and  fascinating  objects  that  can  well  be  imag- 
ined. We  shall  thus  see  the  frustule  without  sensible  distortion 
the  striae  displayed  with  such  exquisite  beauty  of  definition  as 
must  command  your  admiration,  and  minus,  too,  the  suspicion 
of  a  diffraction  line  I 

The  attention  of  Andrew  Boss,  while  examining  Podura 
scales  with  glasses  of  his  own  manufacture,  was  called  to  the 
thickened  edge,  the  "•  Nasmyth  membrane  "  so  plainly  seen  with 
the  non-adjustable  glass  he  then  employed,  and  to  him  are  we 
indebted  for  the  collar  adjustment  now  so  common  to  all  first- 
class  objectives. 

Now,  my  friends,  good  object-glasses,  like  astronomers,  have 
their  "  personal  equation."  They  alone  are  the  ones  to  be  most 
affected  by  collar  adjustment;  an  ordinary  glass,  furnished 
with  compensating  screw,  is  scarcely  superior  to  an  ordinary 
non-adjustable  lens ;  one  may  turn  the  collar  through  its  entire 
range,  without  sensible  or  corresponding  change  in  definition. 

me  saying  that  he  was  surprised  that  Dr.  Woodward  should  have  allowed 
the  publication  of  prints  giving-  such  indifferent  ideas  of  the  work  of 
American  lenses.  I  replied,  that  as  I  then  understood  the  mat1  er,  it  was 
Col.  Woodward's  intention  to  show  the  work  of  the  objective  purposely 
placed  out  of  adjustment,  and  I  so  continued  to  think  at  the  date  of  the 
above  lecture,  a  fact  obvious  to  the  reader.  I  also  su-rgested  that  the  litho- 
graphs might  not  fairly  represent  the  photographs  ;  that  if  it  was  the  case, 
Col.  Woodward  would  surely  make  the  fact  known.  His  silence,  however, 
authorized  the  inference  that  the  original  photos  had  not  suffered  at  the 
hands  of  the  lithographer.  I  th  nk  I  can  now  safely  affirm  that  the  general 
opinion  is  that  one  of  these  lithographs  was  intended  by  Col.  Woodward  to 
give  a  correct  idea  as  to  the  appearance  of  P.  S  ixonica  when  property 
resolved,  i.  e.,  that  it  might  be  contrasted  with  the  others  then  presented. 
Be  all  this  as  it  may,  I  am  prepared  to  asse- t  that  no  one  of  said  lithographs 
gives  any  idea  of  the  proper  resolution  of  Fr  istulia  Saxonica.— J.  E.  S.. 
January,  1878. 


SUPPLEMENT.  391 

On  the  contrary,  objectives  of:  the  widest  apertures,  and  capable 
of  yielding  intense  definition,  require  the  strictest  attention  to 
their  adjustment.  * 

Nor  is  this  all.  It  is  quite  possible  to  accurately  adjust  a  first- 
class  objective,  and,  nevertheless,  in  this  very  act  defeat  the 
maximum  performance  of  a  first-class  glass  1 

When  working  with  oblique  light,  the  maximum  performance 
of  a  superior  glass  will  be  obtained  at  maximum  aperture  ;  if 
this  maximum  aperture  obtains,  with  the  systems  '•  closed,"  as 
is  often  the  case,  it  is  then  manifestly  our  business  to  use  covers 
of  such  thickness  as  will  "  correct"  the  objective  at  "  closed," 
and  to  work  such  a  glass  over  thinner  covers,  requiring  the  lens 
to  "  correct "  at,  or  near  bk  open  point,"  would  surely  defeat  its 
best  performance. 

It  being  possible  that  we  may  have  time  in  the  course  of  the 
evening  to  practically  discuss  this  point,  I  have  brought  here  an 
objective  which,  in  any  position  of  its  collar,  has  plus  180°  of 
aperture  ;  its  balsam  angles  are  at  "  closed,"  97i°;  at  half  way 
between  "  open  "  and  4*  closed  "  95°  ;  at  open  point,  85°.  It  will 
be  an  easy  matter  to  demonstrate  that  this  glass  is  defeated  by 
the  thin  covers  of  the  Moller  plates,  over  which  the  glass  will 
"  correct "  near  to  "  open  point,"  and  conversely,  of  the  decided 
increase  of  definition  obtained  (and  angle  also)  when  worked 
through  a  supplemental  cover  of  sufficient  thickness  to  cause 
adjustment  with  the  systems  at,  or  near  "  closed." 

I  have  brought  here  another,  and  a  totally  different  objective; 
this  glass  has  a  constant  bals,im  angle  of  100°  through  nearly 
the  whole  run  of  its  adjusting  screw.  Manifestly,  when  using 
this  glass,  there  need  be  less  attention  paid  to  the  thickness  of 
cover,  a  fact  which  is  demonstrated  in  practice. 

*  In  an  article  contributed  by  Mr.  P.  B.  Wenhana— see  London  Microsr.op- 
icalJournal  for  March,  1876—1  read,  as  follows  :  "The  adjustment  seems  to 
be  a  stumbling-  block  for  those  advocating  an  extra  immersion  theory.  We 
have  now  in  use  thousands  of  serviceable  im  nersion  object-glasses,  capa- 
ble of  denning  most  tests,  and  whic-i  have  no  adjustment,  as  they  are  set 
for  an  average  thickness  of  cover.  They  answer  well,  because  in  the  im 
mersion  system  the  errors  of  cover  aberrations  ara  nearly  eliminated,  and 
with  a  balsam  intermedium  they  would  be  inappreciable."  (Ill) 

—  J.  E.  S. 


392  HOW   TO    SEE    WITH   THE   MICROSCOPE. 

These  two  objectives  were  constructed  expressly  for  me,  and 
were  especially  intended  for  conjunct  use— they  are  in  truth, 
companion  glasses ;  either  of  them  will  display  the  19th  band 
by  oblique  use  of  artificial  light,  and  also  the  markings  of  An- 
gulata  by  central  lamp  illumination.  Of  the  two,  the  first- 
named  has  the  greatest  working  distance,  and,  for  reasons 
already  given,  will  work  at  maximum  performance  over  covers 
l-50th  of  an  inch  in  thickness,  and  in  the  hands  of  one  thor- 
oughly conversant  with  its  functions,  it  is,  perhaps,  the  most 
generally  useful  glass. 

I  have  here  still  another  objective  of  plus  180°  of  aperture. 
This  glass  was  intended  to  be  a  compromise,  and  to  serve  to  a 
great  degree  the  purposes  both  of  the  l-6th  and  the  l-10th  before 
mentioned.  The  glass  I  now  refer  to  has  at  u  closed  "  a  balsam 
angle  of  97£ ;  at  open  point,  92.  The  compromise  is  thus  appar- 
ent :  this  l-6th  was  made  to  my  order  for  the  gentleman  who  tills 
the  executive  chair  of  this  society.  It  asks  no  favors  of  M. 
Kobert,  nor  of  a  centrally  posed  Angulata,  and  when  one  is  con- 
fined to  a  l-6th  alone,  a  glass  of  this  construction  will  prove  of 
great  value. 

These  conditions,  which  have  still  greater  force  when  we 
include  the  work  of  various  opticians,  need  attention  and  study 
in  default  of  which  you  may  expect  diffraction  lines  and  dif- 
fraction borders;  and,  perchance,  our  old  friend,  the  fct  Nas- 
myth,"  may  put  in  an  appearance ! 

I  repeat,  that  it  was  the  dominant  purpose  of  these  desultory 
remarks  to  call  your  attention  to  the  importance  of  microscope 
instrumentation,  and  to  the  manipulations  connected  therewith. 
To  the  fact  that  it  is  a  study,  a  profession  in  itself,  and  an 
accomplishment  that  must  be  fully  mastered  at  the  outset, 
before  one  can  investigate  with  precision,  or  have  claim  to  the 
confidence  of  others.  In  point  of  fact,  the  most  expert  manip- 
ulator will  constantly  have  something  to  learn— there  is  no 
landing  place  where  one  can  stop  and  rest.  The  world  pro- 
gresses, and  so  should  the  microscopist— pari  passu. 

I  take  it  for  granted  that  nothing  I  have  said  will  lead  you  to 
suppose  that  I  am  opposed  to  the  legitimate  use  of  low-angled 
objectives;  nothing  could  be  further  from  my  purpose.  When 


SUPPLEMENT.  393 

properly  used,  for  preliminary  examinations,  they  are  convenient 
and  useful,  but  for  advanced  work  they  should  be  abandoned, 
and  in  favor  of  more  inconvenient  glasses  of  wider  apertures. 

A  wide-angled  lens,  incapable  of  receiving  and  utilizing  cen- 
tral beams,  is  a  faulty  and  undesirable  objective  ;  it  is,  in  fact, 
but  half  a  glass.  And  on  the  other  hand,  a  low-angled  objec- 
tive, incapable  of  receiving  lateral  beams,  is.  in  my  opinion, 
•equally  undesirable,  unless,  indeed,  when  we  are  prepared  to 
sacrifice  force  of  definition  to  convenience  of  handling. 

It  must  be  admitted  that  there  are  functional  and  character- 
istic differences  in  the  performance  of  the  two  classes  of  objec- 
tives; for  instance,  a  wide-angled  glass  of  relatively  shorter 
focal  length  will  not  see  so  far  around  an  object  as  will  one  of 
narrow  aperture  and  longer  focal  distance.-  This,  as  well  as 
•other  considerations  which  might  be  mentioned,  offer  no  rebut- 
ting testimony  to  the  statement  already  advanced,  that  the 
principal  advantage  presented  by  the  low  angles  is  their  con- 
venience in  manipulation. 

In  conclusion,  I  have  to  thank  you  for  your  kind  attention  to 
the  rambling  remarks  I  have  had  the  honor  of  presenting.  Dur- 
ing the  few  short  hours  that  I  have  been  in  your  city,  the  earth 
has  not  had  time  to  make  one  rotation  ;  but  I  have  had  a  plenty 
-of  time  to  experience  and  enjoy  a  generous  hospitality.  I  am 
now  ready  to  show  you  the  promised  objects,  and  shall  be  happy 
to  see  what  you  have  to  offer.  You  will  find  me  ready,  willing 
and  ardent  to  be  taught,  and  in  microscope  matters  be  assured 
I  am  as  absorbent  as  a  sponge. 

A  CHAPTER  ON  ELEMENTARY  PHYSICS. 
(Dedicated  to  Prof.  Hitchcock.) 

Part  First— The  Sun.— u  The  luminous  orb,  the  light  of 
which  constitutes  day ;  the  central  body  around  which  the  earth 
and  planets  revolve  ;  a  celestial  body  which  can  be  seen  almost 
any  fair  day  through  a  piece  of  smoked  glass." 

I  beg  my  friend  to  read  the  above  little  monograph  on  ele- 
mentary astronomy  carefully.  Assuming  his  compliance  with 
this  request,  I  go  on  to  say  that  just  after  sundown  this  evening, 
my  attention  was  called  to  his  really  kind  notice  of  myself,  as 


394  HOW    TO    SEE    WITH   THE    MICROSCOPE. 

well  as  my  Dunkirk  lecture.  Allow  me  to  assure  you,  my  dear 
professor,  that  although  we  have  been  pulling  at  opposite  ends 
of  the  rope  for  some  months,  the  generosity  I  have  experienced 
at  your  hands  has  been  vastly  in  advance  of  what  I. could  have 
returned,  and  has  placed  me  in  position  to  receive  any  criticism 
that  you  might  offer  with  the  best  possible  grace. 

I  now  propose  to  jerk  my  end  of  the  rope  in  a  manner  that 
will  make  things  lively  with  you  I  The  fact  is,  when  I  get 
after  you  with  a  "  sharp  stick  "  you  become  unusually  brilliant 
with  the  jerk  responsive  1  I  like  it. 

I  admit  that  you  are  one  "  who  demands  accuracy  of  expres- 
sion in  every  branch  of  science"  —  "that  the  scientist  has  no 
right  to  say  what  he  does  not  mean,  and  he  has  no  right  to  pre- 
sume that  his  readers  will  understand  him  if  he  uses  incorrect 
language."  I  therefore  have  placed  the  above  little  monograph 
on  elementary  astronomy  at  your  service,  and  in  timely  season r 
fearing  otherwise  you  might  be  led  astray  by  my  use  of  th& 
word  "  sundown  "—you  will  see  the  point.  It's  true  that  Joshua 
of  old  commanded  the  sun  and  moon  to  stand  still,  and  the-' 
story  is  found  in  a  book  generally  admitted  to  be  a  classic,  but 
— no  matter. 

Now,  professor,  I  fear  that  you  do  not  practice  what  you 
preach ;  for  I  read  (page  92),  "  if  this  question  were  put  to  a 
thorough  physicist  *  *  *  knowing  nothing  about 
balsam  or  fluid  mounts,  etc."  Isn't  there  an  "  impossibility  'r 
here  ?  A  thorough  physicist  knowing  nothing,  etc.  There's  a 
screw  loose  somewhere. 

liight  on  your  next  line  is  another  jumble.  Here  is  a  want  of 
accuracy  or  what  not  —  which  is  it  ?  You  say  "  Must  the  scien- 
tist be  led  by  the  nose,"  etc.  If  this  expression  is  accurate,  1 
want  you  to  tell  me  just  how  this  kind  of  a  thing  is  accom- 
plished ;  give  me  the  p-r-a-c-t-i-c-a-l  details,  just  as  it  would  be 
done  in  the  flesh,  including  the  "  adopt "  and  the  "  teach  'r 
—  before  an  audience,  too,  without  "  apology  " — and  the  why  of 
it.  "  It's  the  right  and  duty  of  every  man  of  science  to  ask  this 
little  question  whenever  it  occurs  to  him."  "  The  scientist  has  no- 
right  to  say  what  he  does  not  mean."  Let  us  have  the  facts. 

Part  Second.— 180°,  plus  180°,  180°  -f  45.°    It  is  true,  my  dear 


SUPPLEMENT.  395 

sir,  that  in  my  Dunkirk  lecture  I  did  use  the  words  u  plus  180° 
of  aperture/'  Now  that  select  and  intelligent  audience  (com- 
prising physicists  who  did  know  something  about  "  balsam 
angles,")  so  far  from  demanding  an  "  apology,"  generously  and 
unanimously  gave  me  a  vote  of  thanks.  Curious,  wasn't  it  ?  I 
remember  well  my  delight  in  there  meeting  the  veteran  Dr.  J. 
W.  Armstrong,  Principal  of  the  Fredonia  Normal  School,  and 
one  of  the  leading  educators  of  your  state;  another  physicist, 
too,  who  can  talk  intelligently  as  to  "  balsam  angles,"  and  who- 
has  made  the  apertures  of  objectives  an  especial  study,  and 
who  afterwards  became  one  of  my  most  valued  correspondents. 
Nor  did  we  have  any  quarrel  about  the  "  plus  180Q."  Most  of 
the  audience  had  read  about  Joshua,  and  doubtless  would  not 
baulk  at  such  expressions  as  "  sunrise  ''  or  "  sunset." 

After  all,  professor,  admitting  that  the  "  plus  180°  "  might 
have  courted  sor~.e  such  gentlemanly  criticism  as  it  finally  got 
from  you,  I  reckon  I  was  as  near  right  as  Joshua.  But  before  I 
can  lift  you  over  this  stile,  I  must  s.coop  you  up !  get  you 
together  in  some  shape,  so  you  can  be  handled.  First  of  allT 
you  seem  to  put  the  180°,  plus  180°,  180°  x  45°,  all  in  one  boat 
together;  you  regard  them  as  synonyms.  And,  secondly,  I 
have  to  learn  some  things  from  you. 

Messrs.  Tolles  and  Spencer  you  denounce  because  they  mark 
their  objectives  180°,  which  you  say  is  not  only  •"  impossible,"" 
but  "  absurd,"  and  that  one  of  these  gentlemen  (you  don't  say 
which)  attempts  to  lead  the  scientist  "  by  the  nose."  And  you 
further  say  that  one  ot  them  (I  don't  know  which,  again,) 
"  might  as  well  add  45°  to  said  180°. 

Well,  here  is  material  enough  to  commence  on.  Now,  my 
dear  professor,  you  maintain  it  to  be  the  "  right  and  duty  "  even 
of  every  man  of  science  to  ask  this  little  question  whenever  it 
occurs  to  him  the  "  why"  part  you  know).  That  I  have  been 
engaged  in  a  controversy  with  you  for  months,  demonstrates, 
my  claim  as  a  "  man  of  science."  You  can't  dodge  that,  and 
the  "occur  "  part  is  present  and  up  to  the  high-pressure  notch. 

Now,  I  want  to  know  "  why  "  it  is  that  180°  of  aperture  is- 
impossible ;  "why  "  that  plus  180°  of  aperture  is  impossible  and 
absurd.  We  have  your  assertions,  but  minus  the  ghost  of  a  dem- 
onstration. 


396  HOW   TO   SEE   WITH   THE   MICROSCOPE. 

Why  do  you  accuse  Messrs.  Tolles  and  Spencer  of  perpetrat- 
ing acts  that  are  absurd  and  impossible ;  and  why  do  you  ven- 
ture to  hint  that  one  of  these  gentlemen  attempts  to  "  lead 
scientists  by  the  nose,"  (whatever  that  may  mean).  The  names 
of  Spencer  and  Tolles  are  revered  by  American  microscopists, 
and  their  unrivaled  efforts  in  the  improvement  of  object-glasses 
have  won  for  them  a  world-wide  reputation.  The  chances  are 
that  they  know  more  of  microscope  optics  than  you  and  I  put 
together;  and  these  are  the  men  who  mark  their  objectives 
4t  180°."  Why  should  there  be  kt  a  law  to  prevent  it  V" 

Now,  professor,  if  this  18*0°  is  impossible  and  absurd,  will  you 
kindly  inform  the  readers  of  this  journal  what  figures  Tolles 
and  Spencer  ought  to  engrave  on  their  wide-angled  objectives 
in  place  of  the  awful  tfc  180°."  Will  you  be  kind  enough  to 
name  the  extreme  angle  immediately  adjacent,  but  not  contact- 
inQ  the  impossible  and  the  absurd  ? 

Again  I  read,  "  plus  180°  does  riot  mean  97°  balsam."  Did  I 
assert  this  V  Now,  I  ask  what  does  97°  balsam  mean  ?  Let's 
have  it,  and  the  awhy"  thereof.  Unless  you  can  tell  me  exactly 
what  the  97°  balsam  angle  is,  I  shall  not  take  any  stock  in  your 
above  assertion. 

Once  more,  you  say  that  "true  apertures  can  be  measured 
and  definitely  stated."  I  wish  that  you  would  tell  Mr.  Wenham 
how  the  thing  is  done ;  he  tried  for  a  whole  year  to  measure  one 
of  Tolle's  objectives,  without  getting  any  two  results  alike ! 
But  I  am  after  you,  not  Wenham.  I  desire  to  learn  irom  you 
precisely  what  "  true  aperture  is."  When  thus  taught,  then  1 
desire  to  know  by  what  physical  process  the  same  can  be  meas- 
ured— "  definitely"  you  know.  "Accuracy"  is  the  thing  we 
scientists  want. 

Now,  my  dear  sir,  I  call  on  you  to  answer  all  of  these  inter- 
rogatories, and  when  you  shall  have  proven  that  180°,  plus  180°, 
or  180°  X  45°,  are  one  and  the  same  thing ;  when  you  shall 
show  that  Messrs.  Tolles  and  Spencer  are  asserting  absurd  and 
impossible  things,  and  more,  are  trying  to  lead  scientists  "  by 
the  nose ;"  when  you  shall  prove  that  a  thorough  physicist 
can  know  nothing  of  balsam  or  fluid  mounts ;  when  you  shall 
have  demonstrated  that  I  should  have  apologized  to  my  Dun- 


SUPPLEMENT.  397 

kirk  audience  ;  when  you  shall  have  proven  what  97°  of  balsam 
angle  is ;  ditto  as  to  "  true  aperture,"  and  how  to  "definitely 
measure  "  the  same— then  and  riot  until  then  will  I  take  the 
"plus  180°  "  under  advisement.  Meanwhile  we  will  be  good 
friends,  and  with  Gen.  Grant  say,  "  Let  us  have  peace."  Don't 
omit  reading  the  reprint  of  Wenham's  article  on  angular  aper- 
ture, pages  74  and  75. 

CHOICE  OF    OBJECTIVES. 

Ed.  Am.  Jour.  Microscopy.— It  was  with  real  pleasure  that  I  read 
the  article  entitled  "  Dr.  Carpenter  on  Angular  Aperture,"  by 
W.  G.  Lapham,  Esq.,  in  your  May  issue. 

First  of  all,  it  is  very  satisfactory,  from  the  fact  that  Mr. 
Lapham  speakes  from  a  practical  standpoint.  The  gentleman  is- 
an  entire  stranger  to  me,  but  the  fact  that  his  conclusions  are 
drawn  from  his  personal,  and,  I  doubt  not,  protracted  experi- 
ence, is  evident  from  the  ability  with  which  he  handles  his- 
subject. 

Your  readers  are  well  aware  that  I  have  often  complained 
that  I  have  been  compelled  to  fight  theory  with  practice  and 
that  no  effort  on  my  part  sufficed  to  induce  my  opponents  to 
abandon  their  theoretical  ideas,  and  to  examine  practically  as  to 
the  truth  of  the  positions  advanced  by  myself.  In  Mr.  Lap- 
ham,  however,  I  resognize  a  co-worker,  and  althiugh  the 
results  he  arrives  at  are  not  in  perfect  coincidence  with  my  own, 
I  find  nothing  to  criticize,  but  am  simply  desirous  of  further 
comparing  notes  with  the  gentleman,  in  the  hope  that  some- 
thing to  the  advantage  of  microscopy  may  be  developed. 

I  propose  to  present  a  few  thoughts  for  Mr.  Lapham's  con- 
sideration, requesting  the  gentleman  to  give  them  whatever 
study  and  attention  he  may  elect,  and  to  advise  your  readers- 
as  to  the  conclusions  he  arrives  at;  and,  as  before  intimated, 
nothing  that  I  have  to  say  ought  to  be  taken  in  the  light  of  a 
criticism  of  his  really  excellent  paper. 

First,  I  desire  to  ask  if  Mr.  Lapham  does  not  attach  too  much 
importance  to  the  so-called  "  penetration."  Is  there  in  esse,  any 
such  thing  as  "penetrations?"  Perhaps  it  will  be  well,  first  of 
all,  to  settle  this  point. 


398  HOW   TO    SEE   WITH   THE    MICROSCOPE. 

Now  I  hold  as  follows :  We  will  take,  for  example,  two  glasses, 
both  possessing  the  same  amplifications  and  the  same  apertures ; 
now  of  these  two  glasses,  the  one  having  the  greater  working 
distance  will  exhibit  structures  situated  slightly  out  of  the 
precise  focal  plane,  or  what  amounts  to  the  same  thing,  will  be 
less  susceptible  to  slight  changes  in  the  focal  distance,  or  again, 
to  use  the  words  of  Dr.  Carpenter,  will  have  the  greater  pene- 
tration. In  extreme  cases,  the  item  of  aperture  may  be  dis- 
regarded. For  instance,  as  stated  in  my  Dunkirk  lecture,  a 
spectacle  lens  of  sixty  inches  focal  length  will  be  endowed  with 
greater  penetration  than  a  To'les  duplex  objective. 

But  in  the  Dunkirk  address,  I  did  not  avail  myself  fully  «£ 
the  demonstration  afforded  by  the  spectacle  lens,  but  now 
invite  Mr.  Lapham's  attention,  thus  :  If  it  so  be  that  with  the 
spectacle  lens  I  am  enabled  to  see  with  perfect  clearness  of 
vision  objects  across  the  road,  it  will  surely  occur  that  when  I 
attempt  to  read  fine  print,  that  the  lens  will  defeat  me.  I  will, 
to  be  sure,  see  the  lines  of  the  print,  will  recognize  the  contour 
of  the  book,  and  larger  objects  in  immediate  proximity,  etc. 
Here  is  an  example  from  everyday  life,  to-wit :  The  glasses 
suitable  for  reading  will  not  answer  for  observations  at  a  dis- 
tance. True  it  is  that  with  such  glasses,  with  which  we  read 
with  ease,  we  may  also  see  the  general  forms  of  things  across 
the  road,  yet  they  suffice  not  to  render  clearly  the  details  thereof. 
Hence  we  have  all  of  us  observed  that  many  persons  wearing 
•convex  glasses  often  use  two  pairs  of  spectacles,  one  for  near 
and  one  for  distant  vision. 

Now  in  this  everyday  case  we  are  taught  a  ICLSOH,  that,  from 
some  cause  or  other,  has  been  a  slow  one  to  acquire.  First 
**  penetration,"  in  its  naked  aspect,  is  simply  a  function  depend- 
ing upon  working  distance ;  and  secondly  that  "penetration," 
unless  acccmpartied  with  a  certain  amount  of  definition*  is  practi- 
cally worthless.  I  ask  Mr.  Lapham's  close  attention  to  this  point, 
one  that  has  been  terribly  overlooked. 

Now,  if  Mr.  Lapham's  one-sixth  of  180°  happens  to  just 
"  turn  the  corner,"  i.  e.  have  balsam  angle,  say,  about  85°,  I 
would  feel  sure  that  a  little  observation  would  lead  him  to  the 
same  opinions  I  have  arrived  at,  and  I  only  fear  that  he  has 


SUPPLEMENT.  399 

chosen  one  of  the  highest  balsam  angles,  in  which  case  he  will 
have  to  fall  back  on  his  four-tenths.  Nevertheless,  let  him,  if 
he  will,  try  the  experiment,  and  report  as  to  whatever  is  gained 
in  point  of  penetration  by  the  use  of  his  one-forth  of  50°  over 
and  above  what  can  be  obtained  by  the  use  of  the  one-sixth,  or 
the  four-tenths.  The  point  I  have  to  make  is  this— the  one- 
fourth  of  50°  will  have  the  greater  penetration  (so-called,  like 
the  spectacle  lens)  but  will  lack  definition,  to  the  end  that  more  is 
lost  in  the  latter  element  than  is  gained  in  the  former. 

I  state  as  a  matter  of  fact,  but  with  no  desire  to  bias  the 
further  observations  of  Mr.  Lapham,  that  I  have  used  just  such 
a  one-fourth  as  he  describes,  but  have  ultimately  discarded  it, 
and  in  favor  of  a  one-sixth  marked  by  the  maker  180Q,  which  I 
find  will  do  all  the  work  (penetration  included)  of  the  one-fourth 
of  50°  and  a  great  deal  more  besides.  But  behind  this  one-sixth, 
I  hold  a  one-tenth  of  100°  balsam  angle  in  reserve,  for  work 
where  "  penetration"  is  ruled  out. 

As  to  the  other  point  suggested.  Is  there  not  undue  weight 
attached  to  this  "penetration?"  With  me,  I  have  often  been 
obliged  to  take  special  measures  to  get  rid  of  this  function,  and 
for  this  purpose  use  the  Beck  illuminator,  which  gives  me  only 
surface  structures.  I  mention  the  fact,  but  am  willing  to  admit 
that  a  certain  amount  of  "  penetration"  is  at  times  desirable, 
and  should  be  provided  for  as  perfectly  as  possible. 

Mr.  Lapham  recommends  a  four-tenths  of  100°.  I  have  often 
thought  that  such  a  glass,  or  a  half-inch  of  the  same  angle, 
would  be  desirable,  and,  as  a  luxury,  arn  still  of  the  opinion.  It 
must  be  remembered  that  he  very  properly  rules  out  the  item 
of  cost ;  wnile  on  the  other  hand  I  have  made  it  a  study  to  avoid 
expense,  where  my  opinion  has  been  solicited  in  the  matter  of 
selection  of  objectives. 

Mr.  Lapham  recommends  a  certain  number  of  low-angled 
glasses,  all  others  to  be  of  the  highest  angles,  and  of  the  best 
quality  and  well  corrected.  Why  not  amend  this  by  insisting 
that  all  glasses  have  the  highest  attainable  angles?  selecting 
of  such  the  one  suitable  for  the  work  in  hand. 

Again,  Mr.  Lapham  states  that  we  have  no  need  to  consider 
objectives  of  lower  power  than  the  half-inch  for  "  they  are  not 


400  HOW   TO    SEE    WITH   THE    MICROSCOPE. 

made  with  angles  sufficiently  high  to  injure  penetration."  Here 
is  involved  an  error  in  fact,  one  quite  pardonable  too.  Not  long- 
since  a  German  gentleman  remarked  to  the  writer  that  it  seemed 
to  him  that  when  the  London  opticians  demonstrated  a  certain 
opticial  law,  some  Yankee  optician  would  be  just  mean  enough 
to  make  an  objective  that  would  upset  the  whole  arrangementl 
And  it  is  perforce  of  this  fact  that  Mr.  Lapham  becomes  involved 
in  his  very  pardonable  error.  Now  I  have  in  my  possession  a 
two- thirds  of  the  Messrs.  Spencers  of  48°  aperture.  They  have 
lately  made  to  my  order  an  inch  of  47°.  The  clear  diameter  of 
both  glasses  is  about  the  same;  the  working  distance  of  the 
two-thirds  is  25-100ths  of  an  inch,  while  that  of  the  inch  is  but 
13-100ths  of  an  inch,  and  the  '"penetration"  of  the  latter  (so- 
called)  is  less  than  that  of  the  2-3ds.  In  fact  the  penetration  of 
the  inch  is  ''injured,"  as  compared  with  one  of  30°.  The  reader 
will  notice  that  Mr.  Wenham's  pet  theory  gets  also  into  grief. 
I  assure  Mr.  Lapham  that  this  new  inch  is  a  glorious  glass,  pene- 
tration or  no  penetration. 

Finally,  I  desire  to  extend  to  Mr.  Lapham  personally  my 
thanks  for  his  instructive  and  interesting  article.  It  will  be  a 
pleasure,  and,  I  doubt  not,  profit  to  compare  notes  with  himr 
and,  in  the  words  of  my  very  generous  opponent,  Prof  Hitch- 
cock, I  will  add  that  all  I  desire  is  "the  facts."  Mr.  Lapham r 
by  the  way,  will  be  pretty  sure  to  catcli  it,  about  that  180Q,  from 
Prof.  H.,  on  the  "  impossible"  and  the  "  absurd." 

It  may  be  well  enough  to  add  that  my  first  impulse  was  to- 
write  Mr.  Lapham  privately  for  an  interchange  of  personal 
experiences,  but  on  reflection  chose  this,  the  more  public  plan, 
hoping  to  enlist  the  attention  of  others  in  the  same  direction. 

OLEOMARGARINE  AGAIN. 

Ed.  Am.  Jour.  Microscopy:— The  article  giving  "  The  Micro- 
scopical Examinations  of  Oleomargarine,"  by  Prof.  Michels, 
which  appeared  in  a  recent  issue  of  this  journal,  was  perused 
by  me  with  much  interest,  and  I  at  once  resolved  to  repeat  the 
experiments  as  detailed. 

The  first  thing  requisite  was  to  secure  authentic  specimens  of 


SUPPLEMENT.  401 

oleomargarine.  In  order  to  do  this,  I  solicited  the  friendly  aid 
of  a  prominent  gentleman  of  this  city,  who  is  also  well  known 
in  business  circles  in  New  York.  I  also  wrote,  independentlyT 
to  a  gentleman  in  your  city,  urging  him  to  obtain  for  me  the 
samples  required. 

Desiring  also  to  procure  a  specimen  of  genuine  dairy  butter, 
I  applied  to  a  well-known  citizen  of  this  city,  who  procures  his 
supplies  directly  from  a  farmer. 

After  an  interval  of  ten  days,  I  was,  in  response  to  my  solici- 
tations, in  possession  of  three  samples  of  oleomargarine,  and 
one  sample  of  pure  dairy  butter.  The  three  samples  of  oleo- 
margarine are  directly  from  the  manufacturers  at  Xew  York 
city,  and  will  be  referred  to  as  Nos.  1,  2,  and  3. 

The  four  samples  were  subjected  to  examination  under  the 
microscope ;  tha  objectives  used  were  a  l-4th  inch  of  100°  by 
Tolles,  and  Spencers  late  duplex  l-4th  of  180°. 

Samples  Nos.  1,  2  and  3,  and  also  the  specimen  of  pure  dairy 
butter,  showed  many  crystals  of  chloride  of  sodium  ;  the  crys- 
tals furnished  by  the  pure  butter  were,  however,  cleaner,  and 
more  acceptable  generally  than  those  exhibited  by  Nos.  1, 2 
and  3. 

Samples  Nos.  1,  2  and  3,  in  addition  to  crystals  of  chloride  of 
sodium,  displayed  other  crystals,  those  of  nitrate  of  soda  being 
prominent ;  while  forms  closely  resembling  crystals  of  choleste- 
nne  were  found  in  considerable  numbers. 

Regarding  Nos.  1,  2  and  3,  it  may  be  remarked  that  Nos.  1 
and  2  were,  to  outward  appearance,  tolerably  fair  imitations  of 
genuine  butter,  and  might  by  the  ordinary  purchaser  be  accept- 
ed and  bought  as  such.  N"o.  3  was  a  poorer  counterfeit,  and 
would  probably  be  rejected  by  most  buyers ;  but  if  mixed  in 
equal  parts  with  the  genuine  article,  the  mixture  would  be  likely 
to  deceive  the  purchaser. 

In  samples  Kos.  1  and  2  the  microscope  displayed  the 
•'  feathery  crystals"  (margarine)  described  by  Prof.  Michels, 
although  these  were  not  constantly  present  in  every  field  exam- 
ined. By  moving  the  slide,  other  fields  were  brought  to  view  in 
which  these  crystals  were  much  more  prominent  than  those 
given  in  the  cut  accompanying  Prof.  Michels'  paper.  The  crys- 


402  HOW    TO   SEE    WITH   THE    MICROSCOPE. 

tals  of  nitrate  of  soda  and  cholesterine  (?)  were  to  be  seen   in 
every  slide  prepared  from  the  samples  named. 

Besides  the  crystals  named,  samples  Nos.  1  and  2  gave  "  sus- 
picious cells  "  in  large  numbers,  accompanied  by  shreds  and 
tissue  fibres,  many  in  a  broken  down  condition,  while  others 
seemed  to  be  in  a  tolerably  normal  stdte,  sufficient  almost  to 
establish  the  presence  of  voluntary  muscle.  Bundles  of  these 
fibres  were  closely  examined  with  the  duplex  l-4th,  under  powres 
as  high  as  1,600  diameters,  with  the  endeavor  to  bring  out 
the  transverse  markings ;  this  was  not  accomplished— owing, 
doubtless,  to  the  nature  of  the  vehicle  (my  observations  in  this 
direction  will  be  continued).  Many  of  the  bundles  seen  were 
completely  broken  down,  and  the  elementary  fibres  detached. 

Sample  No.  3,  when  examined  under  the  microscope,  displayed 
fewei  f  the  "feathery  crystals;"  nevertheless,  this  was  the 
most  u  buspicious  "  specimen  of  the  three ;  there  were  multi- 
tudes of  "  suspicious  cells,"  shreds  and  patches  of  tissue,  in  a 
more  or  less  broken  down  state.  In  one  field  I  felt  tolerably 
sure  of  finding  encysted  hydatids.  This  slide  unfortunately, 
was  accidentally  destroyed  by  the  water  getting  under  the 
cover. 

To  give  an  intelligent  description  of  this  material  (No.  3) 
would  require  far  more  time  to  its  study  than  I  have  at  my  com- 
mand at  present ;  but  I  hope  to  attack  it  again,  and  at  an  earlr 
day.  Suffice  it  now  to  say  that  this  specimen  contains  verymani 
"  suspicious  "  elements,  and  that  its  behavior  under  the  objec- 
tive (here  I  also  include  Nos.  1  and  2),  is— with  the  exception  of 
the  crystals  of  chloride  of  sodium,  and  the  presence  of  a  few 
fatty  globules— totally  different  from  that  of  pure  dairy  butter. 

The  sample  of  pure  dairy  butter  gave  fields  just  as  represented 
by  Prof.  Michels,  with  the  exception  that  crystals  of  the  chlor- 
ide were  almost  constantly  present. 

Having  established,  to  my  own  satisfaction,  at  least,  the  in- 
tegrity ot  the  observations  of  Prof.  Michels,  I  therefore  hold 
that  the  gentleman  should  be  regarded  in  the  light  of  a  public 
benefactor ;  the  matter  he  has  presented  will  be  found  worth 
serious  and  careful  investigation. 

In  one  of  my  recent  lectures  before  the  medical  class  of  this 


SUPPLEMENT.  403 

College,  on  the  JSntozoa.t  I  quoted  (substantially)  from  Dr.  liob- 
erts,  as  follows : 

"  A  marvelous  light  has  been  thrown  in  recent  years  on  the 
zoological  position  of  the  Entozoa,  chiefly  by  the  researches  of 
Siebold  .and  Van  Beneden.  It  has  been  ascertained  that  the  hy- 
datid  worm  found  in  man,  constitutes  the  encysted  phase  in  the 
developement  of  a  very  minute  tape-worm  which  infests  the 
dog.  The  tape- worm  in  question  is  the  Tcenia,  echinococcus ;  the 
entire  adult  animal  is  so  small  that  it  scarcely  exceeds  the  size 
of  a  millet  seed.  It  consists  of  but  three  segments,  of  which 
three,  the  last  only  is  fruitful.  When  this  segment  arrives  at 
maturity,  it  is  cast  off,  and  a  new  one  developed  in  its  place. 
Myriads  of  these  worms  are  sometimes  found  in  the  intestine  of 
the  dog,  and  their  eggs  are  discharged  in  countless  numbers 
with  the  excrements,  the  eggs  so  discharged  are  scattered  far 
and  wide  ;  and  some  of  them  find  their  way  with  the  food  into 
the  stomachs  of  men  and  other  creatures  suitable  for  their  de- 
velopment. Arrived  there,  the  embryo  is  liberated ;  and  after 
penetrating  the  mucus  membrane,  it  burrows  its  way,  or  is  car- 
ried by  the  blood  current  to  some  distant  organ,  where  it  is 
arrested.  Having  thus  lodged  itself,  it  presently  reappears  as  a 
hydatid  vesicle,  in  which  are  developed  the  echinococci,  as  be- 
fore explained.  Dogs  in  their  turn  become  infested  with  the 
corresponding  tsenia  by  feeding  on  the  offal  of  slaughtered 
sheep,  pigs,  etc.,  which  had  been  infested  with  hydatids.  The 
echinococci  therein  contained  develop  in  their  intestines  into 
the  tsenia  echinococci,  and  thus  the  circle  of  transformation  and 
development  recommences." 

By  similar  cycles  of  transformation  and  development,  do  we 
arrive  at  a  class  of  parasites  known  in  medicine  as  the  ectozoa. 
This  term  may  be  said  to  include,  or  be  applied  to,  worms  or 
larvae  of  insects  that  have  been  introduced  into  the  intestinal 
canal  by  accident.  Animalcules,  such  as  the  hair  worm,  grub 
of  the  fly,  may  be  mentioned ;  also  the  larva  of  the  bee,  the  spi- 
der, etc.  Among  animals,  the  disease  known  popularly  as  the 
botts,  to  which  the  horse  is  frequently  a  victim,  is  caused  by 
such  animals  swallowing  the  ova  of  the  oestrus  or  gad-fly. 

That  oleomargarine  manufactured  from  refuse  animal  fats, 


404  HOW   TO    SEE    WITH   THE    MICROSCOPE. 

in  the  manner  described  by  Prof.  Michels,  and  at  a  temperature 
not  above  120°  F.,  may  be  a  highway  through  which  "  eggs  so 
discharged  "  find  their  way  into  the  stomachs  of  men,  is  too  pal- 
pably evident  to  need  further  comment. 


INDEX. 


Acetate  of  soda,  solution,  329. 

Acme  microscope,  84. 

Adjustable  objectives,  148. 

Adj  ustable  glasses,  129. 

American  stands,  17. 

American  stands  compared 
with  German,  18. 

American  histological  stand',  39. 

Analysis,  chemicals  for,  322. 

Analysis,  chloride  of  sodium, 
328. 

Analysis  for  albumen,  337. 

Analysis  for  glasses,  103. 

Analysis,  earthy  phosphates, 
331 

Analysis,  phosphoric  acid,  330. 

Analysis,  sugar,  332. 

Analysis,  sulphuric  acid,  331. 

Analysis,  urea,  323,  325. 

Analysis  for  sugar,  335. 

Angular  aperture,  what  is  it?  93. 

Angular  aperture  defined,  93, 
370. 

Angular  aperture  illustrated, 
94. 

Angular  aperture,  how  to  meas- 
ure, 95. 

Angular  aperture,  versus  work- 
ing distance,  115, 121. 

Angular  aperture  and  central 
illumination,  361. 

Angular  aperture  and  penetra- 
tion, 118. 

Angle  high  glasses,  103. 

Apparatus  for  micro-chemical 
use,  320. 

Apertures,  angular,  93, 


405 


Aperture,  angular  balsam,  123. 
Artificial  light,  187. 


Balsam  apertures,  128. 

Balsam  angles,  advantages  of, 
141. 

Balsam  angle,  management  of 
257, 

Balsam  angle,  and  working  dis- 
tance, 142. 

Balsam  angle,  low  objective  144. 

Baryta  solution,  324. 

Bausch  &  Lomb's  microscopes, 
50. 

Bausch  &  Lomb's  microscope, 
professional,  53. 

Bausch  &  Lomb's  microscope, 
students,  66. 

Bausch  &  Lomb's  microscope, 
stands,  344. 

Bausch  &  Lomb's  objectives, 
346. 

Beck's  microscopes,  72. 

Beck's  microscope  stands,  347. 

Beck's  vertical  illuminator,  217. 

Beck's  vertical  illuminator,  how 
to  use,  221 

Binocular,  objections  to,  30. 

Binocular,  versus  monocular, 
29. 

Biological  microscope,  68. 

Bull's  eye  condenser,  225. 

Bull's  eye  condenser,  how  to  use, 
227.  ' 

Bullock's  microscope,  first- 
class,  "A.  1."  59. 


40G 


INDEX. 


Bullock's  microscope,  59. 
Bullock's  microscope,  D  stand, 

57. 
Bullock's    microscope,     small, 

best,  67. 
Bullock's  microscope    stands, 

343. 


Carbonate  of  soda,  324. 

Carpenter  on  object  glasses,  97. 

Centennial  stand,  Zentmayers, 
34. 

Centennial  stand  and  A.  1.  com- 
pared, 63. 

Central  light  and  high  angles, 
257 

Choice  of  objectives,  397. 

Choice  of  objectives  for  regular  | 
work,  202, 

Chemicals  for  analysis,  322. 

Chloride  of  sodium,  327. 

Chromate  of  Potash,  327. 

Collar   adjustment,   objections 
to,  208. 

Concentric  rotating  stage,  25. 

Condenser,  Bull's  eye,  225. 

Condenser,  small  diameter,  308 

Contributions  to   the  Medical 
News,  358. 

Covering  glass  guage,  216, 

Covering  glass,  selection  of,  213. 


Daylight,  how  to  use  it,  1*3. 
Diatoms,  examinations  of,  255. 
Diatoms  tor  test,  251. 
Diatoms,  order  for  test,  254. 
Diatoms  resolution  as  objective 

test,  249. 
Diatoms  resolution,  with  high  i 

powers,  245. 
Diatoms  resolution,   with    low  i 

powers,  245.  I 


Diatoms,  resolution,  243. 
Draw  tube,  advantages  of,  136. 
Dry  mounts,  list  of,  305. 
Dry  mounts,  \vith  high  objec- 
tives, 298. 
Duplex  glass,  the  first,  9. 


Essentials  of  a  reliable  stand, 
21. 

Examination  of  morbid  pro- 
ducts, 206. 

Examination  of  urinary  depos- 
its, 203. 

Examination  of  oleomargarine, 
400. 

Eye  pieces,  256. 

Eye  pieces  high,  146. 

Eye  pieces  fittings,  33. 

Eye  pieces  solid,  156. 

Eye  pieces  should  fit  loosely  204. 

Eye  training,  287. 

Eye  training  illustrated,  239. 


Family  microscope,  57. 
Fasoldt's  micrometer,  357. 
Fehling's  solution,  333. 
Ferro  cyanide  of  potassium  so- 
lution, 329. 

Field,  flatness  of,  126. 
Fighting  objectives,  117.  140. 
Flatness  of  field,  126. 
Four  system  glasses,  9. 


G 


Glasses,  high  angle,  103. 
Glasses,  high  angle  history  of 

100, 

Glasses,  testing  aperture,  192. 
German  stands  compared  with 

American,  18. 


INDEX. 


407 


German  student  lamp,  187. 


Handling  objectives.  259. 

High  angles,  103. 

High  angles  balsam,  125. 

High  angles,  discursion  of ,  359. 

High  angles,  objectives,  100. 

High,  eye  piecing.  146. 

High  objectives,  with  dry 
mounts.  298. 

Higher  powers,  work  with,  235. 

History  of  high  angle  objec- 
tives, 100. 

Histological  stand,  39. 


Illumination,  artificial,  187. 
Illumination,  daylight,  183. 
Illumination  small  best,  189. 
Illumination,  sunlight,  186. 
Illumination,  varieties  of,  183. 
Illuminator,  Beck's  vertical,  217 
Illuminator,  modified,  219. 
Illuminator,  Wenharn's  reflex, 

157. 
Illuminator,    Wenham's    with 

sunlight,  191. 

Illuminator,   Woodward's,  163. 
Immersion,  125. 


Kerosene   oil  immersion  lens, 
316. 


Lens,  Tolles'  traverse,  179. 
Lessons  on  seeing  with  the  mi- 
croscope, 261. 
Lesson  first,  261. 


Lesson  second,  262. 

Lesson  third,  265. 

Lesson  fourth,  266. 

Lesson  fifth,  268. 

Lesson  sixth,  270. 

Lesson  seventh,  271. 

Lesson  eighth,  273. 

Lesson  ninth,  274. 

Lesson  tenth,  280. 

Lesson  eleventh,  282. 

Lesson  twelfth,  284. 

Low  balsam  angles,  144. 

Low  powers,  working  with,  225. 


Management   of   high   angles, 

257. 
Manipulations,  microscopic, 

157. 

Marais'  approximate  tubes,  330. 
Measuring  bottle,  324. 
Medium  power  of  glass  144. 
Micrometer,  necessity  for,  252. 
Micrometer,  Fasoldt,  357. 
Micrometer,  Rogers',  356. 
Micro-chemical  apparatus,  320. 
!  Micro-chemical  examination  of 

urine,  318. 

Microscope,  Acme,  84. 
Microscope,  Biiusch  &  Lomb, 

51. 

Microscope,  Beck's,  72. 
Microscope,  Bullock's,  59. 
Microscope,  dissecting,  Beck's 

79. 

Microscope,  "D,"  67. 
Microscope,  economic,  72. 
Microscope,  family,  57. 
Microscope,  first-class  A  1,  59. 
Microscope,  international,  348. 
Microscope,  investigator,  345. 
Microscope,  new  biological,  68. 
Microscope,   new   histological, 

79. 

Microscope,  monocular  vs.  bin- 
ocular, 80. 


408 


INDEX. 


Microscope,  national,  29. 

Microscope,  popular,  72. 

Microscope,  professional,  63. 

Microscope  students,  56. 

Microscope,  Sidle's,  84,  351. 

Microscope  selection,  147. 

Microscope,  Tolles  ,  47. 

Microscope,  Zentmayer,  34. 

Microscope,  use  and  abuse  of 
376. 

Microscopic  manipulations,  157 

Mirrors,  concave,  32. 

Mirrors,  hangings  strong,  38. 

Mirrors  mountings,  32. 

Mirrors,  plain,  31. 

Mirrors  used  as  condensers,  229. 

Mirrors  where  attached,  226. 

Monocular  vs.  binocular,  29, 
80. 

Moller's  test-plates,  measure- 
ments of,  253. 

Mounting  of  objectives,  129. 


Names  of  microscopic  dealers, 

341. 
Robert's  test-plate,  254. 


Objections  to  mechanical  stages 

24. 

Objections  to  binoculars,  30. 
Objectives,  adjustable,  148. 
Objectives,  broad  guage,  230. 
Objectives,  balsam,  141. 
Objectives,  choiceiof,  397. 
Objectives,  Dr.   Carpenter  on 

97. 

Objectives,  fighting,  117, 140. 
Objectives,  high  angle,  97.. 
Objectives,  high  angle,  testing 

ot',107. 
Objectives,  low  balsam  angle, 

144. 


Objectives,  one-sixth  preferred 

to  one-fiftieth,  109. 
Objectives,  immersion,  125. 
Objectives,    experience    with, 

202. 

Objectives,  for  physicians,  207. 
Objectives   for   regular  work, 

202. 
Objectives,  test  with  diatoms, 

249. 
Objectives,  testing  aperture  of 

192. 

Objectives,  testing,  198. 
Objectives,  wide  angle,  what  is 

it  ?  137. 
Objectives,    working    distance 

of,  1Q6. 

Objectives,  mounting,  129. 
Objectives,  oil  immersion,  310, 
Objectives,  Spencer's,  353. 
Objectives,  Tolles',  354. 
Objectives,  performance  of,  368. 
Observer's  position,  246,  289. 
Oil  immersion  objectives,  309. 
Oil  immersion,  objectives, expe- 
rience with,  315. 
Oil    immersion    objectives   of 

Zeiss,  310. 
Oleomargarine     examinations, 

400. 


Penetration  and  angular  aper- 
ture, 118. 

Physicians,  objectives  best  for, 
207. 

Physics,  elementary  hints  on, 
393. 

Pod  ura,  scale  resolution  of,  299. 

Position  of  observer,  246,289. 

Professional  microscope,  53. 


Rising  of  the  object.  276. 


INDEX. 


409 


Reaction  of  urine  with  tests, 

339. 
Rogers'  micrometers,  356. 


Selection  of  covering  glass,  213. 

Selecting  a  stand, 

Sliding  tube,  advantages  of,  44. 

Short  tube  stands,  25. 

Small  light  best,  189. 

Small  kerosene  lamp,  189. 

Society  screw,  232. 

Society  screw  not  sufficient  for 
high  angles,  88. 

Specific  gravity  and  tempera- 
ture, 340. 

Spencer's  objectives,  353. 

Spencer's  one  inch  of  50°,  230. 

Stage,  thin,  improvised,  39. 

Stage  swing  and  mirror  best, 
91. 

Stage,  concentric,  rotating,  25. 

Stage,  mechanical  objections  to 
24. 

Stage,  room  necessary,  26. 

Stage  used  by  the  author,  27. 

Stand,  Acme,  84. 

Stand,  American,  17. 

Stand,  American  Centennial, 
34. 

Stand,  Bausch  &  Lomb's,  50. 

Stand,  Beck's,  72. 

Stand,  Bullock's,  59. 

Stand,  essential  of  a  reliable, 
21. 

Stand,  Economic,  72. 

Stand,  Histological,  79. 

Stand,  "D,"67. 

Stand,  Investigator,  345. 

Stand,  International,  348. 

Stand,  large  and  small,  26. 

stand,  large  "  BB,"  47, 

Stand,  large  "  A,"  48. 

Stand,  new  biological,  68. 

Stand,  new  National,  80. 

Stand,  first  class  "  A.  1."  69. 


Stand,  small  best,  67. 
Stand,  popular,  72. 
Stand,  Sidle's,  84. 
Stand,  Tolles',  47. 
Stand,  students',  49,  56. 
Stand,    small  and  cheap,  best, 

92. 

Stands,  with  short  tubes,  25. 
Stands,  Zentmayer's,  34. 
Students  microscopes,  49,  56. 
Sunlight  illumination,  186. 


T. 

Table  for  work,  229. 

Temperature  and  Urine  specific 
gravity,  340. 

Testing  high  angles,  objective, 
107. 

Thin  stage  necessary,  90. 

Tight  fitting  eye  pieces,  204. 

Tolles'  first  duplex,  9. 

Tolle's  microscopes  and  objec- 
tives, 354. 

Tolles'  traverse  lens,  179. 

Tolles'  large  "  BB  "stand,  47, 

Tolles'  large  "  A  "  itand,  48. 

Tolles'  students'  stands,  49. 

Traverse  lens,  179. 

Tube  casts,,  no  genuine  seen, 
319. 

Tube  sliding,  advantages  of, 
44. 


U. 

Urinnry  constituents,  propor- 
tion of,  339. 

Urinary  deposits,  examinations 
of,  203. 

Use  and  abuse  of  the  microscope 
375. 

V. 

Volumetric  analysis,  318. 


410 


INDEX. 


w. 

Weights  recognised,  321. 

Wenham's  reflex  illuminator, 
157. 

Wide  apertures,  lessons  in  the 
use  of,  261 

Wide  apertures,  management 
of  258. 

Wide  angle  objectives,  137. 

Wide  angle  objectives  and  col- 
lar adjustment.  139. 

Wide  angle  objectives  and  illu- 
mination, 140. 

Wide  angle  objectives  and 
working  distance,  137. 

Work  table,  229. 

Working  with  higher  powers, 
285. 

Working   with  lower  powers, 


Working  distance  of  high  an- 
gles, 137. 

Working  distance  of  high  bal- 
sam angles,  143. 

Working  distance  of  objectives* 
108. 

Working  distance  vs.  angle 
aperture,  115,121. 

Woodward's  illuminator,  163. 

Woodward's  illuminator  modi- 
fled,  experience  with,  177. 


Z. 


Zentmayer's  stands,  34,  355. 

Zentmayer's  American  Centen- 
nial, 34. 

Zentrnayer's  American  Histo- 
logical,  39. 


SPECTACELS ; 

AND  HOW  TO  CHOOSE  THEM. 

BY  C.  H.   VILAS,  A.  M.,  M.  D. 

Professor  of  Diseases  of  the  Eye  and  Ear  in  the  Hahnemann  Medical 

College,     and   Ophthalmic  and  Aural    Surgeon  to 

the   Hahnemann    Hospital, 

Chicago,  etc.,  etc. 

This  book  is  full  of  interest  and  instruction  to  readers  of  all 
classes.  Designed  more  especially  for  the  profession,  it  never- 
theless does  not  deal  in  technicalities  or  obscure  terms  and 
will  doubtless  tind  a  large  demand  among  non-professional 
people. 

In  a  clear  and  comprehensive  manner  it  treats  of  a  most 
important  subject,  a  subject  concerning  which,  far  too  many  er- 
roneous and  dangerous  notions  prevail.  It's  aim  is  to  dissemin- 
ate knowledge,  and  to  prevent  the  common  haphazard  custom 
of  choosing  Spectacles,  a  custom  so  often  disastrous  to  vision  or 
fruitful  to  discomfort.  The  Author  points  out  how,  within  a 
comparatively  recent  period,  what  was  once  veiled  in  mystery, 
has  attained  a  sure  place  among  the  sciences ;  how  the  know- 
ledge of  the  proper  construction,  adaptation,  and  uses  of  Spec- 
tacles has  grown  to  great  proportions,  and  has  led  to  a  revolu- 
tion in  the  treatment  of  eye  affections.  Many  popular  delusions 
will  be  dispelled  by  reading  this  book.  It  is  valuable  alike  to 
the  physician  and  the  layman.  The  former  may  utilize  it  in 
practicing  his  profession  ;  the  latter  will  prepare  himself  to 
avoid  errors  fatal  to  vision. 

All  the  new  and  useful  cases  of  trial  lenses  are  described  and 
illustrated  and  their  respective  merits  and  demerits  are  pointed 
out.  It  is  clearly  shown  how  the  low  prices,  at  which  a  good 
set  of  trial  lenses  can  be  obtained,  will  enable  the  physicians  in 
general  practice  to  give  attention  to  the  titting  of  Spectacles 
and  to  treating  ordinary  defects  of  the  vision,  thus  preventing 
the  frauds  so  often  practiced  by  itinerant  venders. 

The  Author's  well  known  accomplishments  in  this  depart- 
ment of  science,  have  eminently  prepared  him  to  skillfully 
treat  so  important  a  subject.  The  work  is  illustrated  and  full 
of  practical  hints. 

Price  bound  in  cloth,  $1.00. 

DUNCAN  BROS.,  Publishers. 

131  &  133  S.  Clark  St. ,  CHl  CA  G  O. 


THE  NURSE; 

OR, 

HINTS  ON  THE  CARE  OF  THE  SICK; 

INCLUDING  MOTHERS  AND  INFANTS,  AND  A  DIGEST  OF 
DOMESTIC  MEDICINE. 


By  CHARLES  T.  HARRIS,  A.M.,  M.D. 
Elegantly  bound  in  Cloth      -  Price,  60  cents. 

"Every  Nurse  should  have  a  copy." 

"Every  Mother  should  possess  this  useful  work." 

"  It  will  not  hurt  physicians  even  to  glance  over  the  pages  devoted  to 
mothers  and  nurses,  and  this  little  treatise  ought  to  become  one  of  the 
tracts  domiciled  in  every  household."—  North  Am.  Journal  of  Homoeopathy. 

This  is  a  valuable  volume  to  professional  nurses  and  mothers,  the  natural 
nurses.  The  author  strongly  advocates  the  importance  of  intelligent,  self- 
sacrificing  nurses.  The  instruction  the  book  contains  is  clearly  and  con- 
scientiously given.— Boston  Inventors  &  Manufacturers'  Gazette. 

Such  a  work  is  very  much  needed.  Itis  simply  and  clearly  written,  giv- 
ing hints  on  all  the  points  which  a  nurse  ought  to  know.  We  cordially 
recommend  this  little  work  to  the  attention  of  mothers  and  nurses  who  will 
find  it  a  valuable  vade  mecum.— Monthly  Homoeopathic  Review,  London. 

A  neatly  printed,  handsomely  bound  work  of  over  a  hundred  pages, 
written  with  the  endeavor,  as  stated  in  the  preface,  to  make  their  scope 
44  broad»enough  to  cover  the  wants  of  two  classes;  the  conscientious  and 
ambitious  professional  nurse,  and  the  faithful  and  loving  mother."  The 
matter  of  the  worfc,  from  the  introduction  to  the  last  page,  seems  well  and 
carefully  written  and  very  sensible.— Ypsilanti  Sentinel. 

It  is  written  in  simple  and  concise  style  and  free  from  all  technicalities, 
and  abounds  in  valuable  facts  and  directions  to  those  who  have  health  as 
well  as  to  those  who  are  called  to  nurse  in  the  sick  room.  It  is  a  book  every 
mother  could  read  with  profit.  Skilled  and  trained  nurses  are  not  a  ways  in 
reach,  and  the  lives  of  those  deartoihe  family  are  of  ten  imperiled  by  simple 
ignorance  of  what  every  intelligent  person  should  know.  Good  nursing, 
every  intelligent  physician  will  say,  is  of  more  value  than  drugs.  The  hand- 
some little  volume  should  find  its  way  into  many  homes,  and  by  the  intelligent 
observance  of  its  rules,  blessings  alone  will  result.— The  News. 

^B^May  be  ordered  through  your  physician,  or  newsdealer,  or  will  be  sent 
to  you  direct  on  receipt  of  price. 

DUNCAN  BROS.,  Publishers, 

113  Madison  and  131  &  133  Clark  St.,  Chicago. 


HOW  TO  BE  PLUMP. 

OR 

TALKS  ON  PHYSIOLOGICAL  FEEDING. 

BY 

T.  C.  DUNCAN,  M,D., 

Author  of  a  Professional  Treatise  on  Diseases  of  Infants 
and  Children  and  their  Homoeopathic  Treat- 
ment; Editor  "  United  States  Medical 
Investigator,  etc.  etc." 

Finely  bound  in  Cloth  ....          Price,  5O  Cents. 

It  is  an  admirable  work  on  hygiene,  as  far  as  i't  relates  to  eating—  Ohio. 
Farmer. 

These  "  Talks  "  have  their  own  charm,  for  most  of  us  like  to  be  plump. 
—  Women's  Journal,  Boston. 

Certainly  all  thin  people  should  ponder  well  its  suggestions  and  put  them 
into  practice.—  Voice  of  Masonry. 

A  brochure  which  many  persons  of  lean  inclinations  will  be  glad  to  read 
and  may  be  able  to  profit  by.— Banner  of  Light. 

The  little  volume  contains  riuch  sensible  professional  advice  upon 
healthy  and  morbid  digestion,  and  the  occasions  of  it.— Zion's  Herald. 

The  book  is  intended  to  indicate  how  anyone  may  become  fat,  fair  and 
jolly,  and  a  careful  perusal  affords  proof  thst  the  author  is  fully  conversant 
with  his  subject,  and  that  he  has  done  it  full  justice.— The  Cmcdgo  Grocer. 

It  is  a  common  sense  volume,  that  believes  in  rational  and  practic  I 
methods  of  preserving  health,  beautv  and  happiness.  It  is  not  a  receipt 
book  of  impos-ibilities;  it  is  a  bright,  genial  book,  that  understands  itself 
from  first  to  last.— The  Chicago  Cosmopolitan. 

We  do  most  warmly  applaud  its  purpose,  and  especially  commend  its 
philosophy  to  theunnaturaliy  It  an,  and  still  mor  *.  to  mothers  in  the  training 
of  delica  e  children  whose  physical  stamina  hardly  equals  that  of  a  full- 
grown  rye-stalk.  Theirs  is  a  leanness  to  be  built  up  into  steady  strength 
and  picturesque  plumpness  of  limb  and  face.— The  Standard. 

CHICAGO,  Sept  18,  1878. 

The  case  referred  toon  page  45  of  "  How  to  be  Plump"  is  our  little  boy, 
who  was  certainly  rescued  from  death's  door.  This  summer  he  began  to  run 
down  again.  After  Dr.  Dun  an  had  tried  several  medicines  without  benefit 
he  i  gain  advised  "  inunction."  and  again  with  the  same  happy  effect.  The 
little  fellow  is  now  plump  and  well.  CH A i>  LKS  WALES. 

^P~May    e  ordered  through  your  physician,  or  newsdealer,  or  will  be  sent 
direct  on  receipt  of  price. 

DUNCAN  BEOS,,  Publishers, 

113  Madison  and  131  &  133  Clark  St.,  Chicago. 


DOCTOR,  WHAT  SHALL  1 


A 

HAND  BOOK 

OF 

DIET  IN  DISEASE. 

BY  CHAS.  GATCHELL,  M.  D., 
Formerly  Professor  of  Practice,  University  of  Michigan. 

It  is  highly  endorsed  by  the  Profession  and  Medical  Press. 

How  often  do  we  hear  that  same  question.  Doctor;  what  shall  I  eat?  and 
though  there  are  text  books  enough  on  the  Pathology  and  Treatment  of 
Diseases,  there  is  hardly  ever  a  word  found  in  them  about  the  Hygiene  in 
Disease.  Gatchell  as  a  teacher,  found  out  this  want,  and  thus  probably 
originated  this  little  treatise,*  lor  which  we  most  heartily  thank  the 
author.  We  consider  the  recipes  in  it  a  little  Materia  Medica  for  itself,  but 
follow  instructions  closely  ;  not  quantity,  but  quality  of  food  deserves  our 
consideration.  —  North  American  Journal  of  Homcepaihy. 

MILWAUKEE,  Wis. 

"I  consider  your  work  on  "Diet  ii  Disease"  to  be  the  most  practical,  and 

therefore  the  most  useful,  work  on  the  subject  with  which  I  am  acquainted. 

No  physician  should  be  wlthoutit;    every  mother  should  have  it.     It  is  in 

use  in  many  of  the  households  in  which  I  practice."    C.  C.  OUHSTEAD.  M.  D. 

President  of  the  Wisconsin  Hommpathic  Medical  Society. 

"This  work  is  plain,  practical  and  valuable,  It  is  really  a  clinical  guide 
on  diet,  and  one  the  profession  will  find  reliable  and  correct."  —  United 
States  Medical  Investigator. 

"By  far  the  best  work  on  the  subject  in  pur  literature.     I  find  it  of  use 
every  day.    I  want  one  in  every  household  in  which  1  practice." 
Oak  Park,  HI.  F.  G.  FOLSOM,  M.  D. 

"Evidently  much  investigation,  thought  and  carefulness  have  entered 
into  the  production  of  this  work,  and  we  believe  it  to  be  worthy  a  place  in 
every  household."  —  The  Magnet. 

*  *  *  "we  have  carefully  examined  the  work  and  s^all  cheerfully 
recommend  it  for  family  use.  The  directions  as  to  what  food  and  drinks, 
and  modes  of  preparation  are  very  judicious."  *  *  *  Resp.  Yours, 

Janesville,  Wis.  DR.  G.  W.  UHITTENDEN  &  SON 

Professor  Charles  Gatchell's  Manual  of  'DIET  IN  DISEASE'  is  the  best  book 
on  the  subject  for  the  people.  It  contains  in  160  pages  an  astonishing 
amount  of  condensed  information  on  a  subject  of  great  importance,  and 
one  but  little  understood.  Its  style  is  admit  able,  pithy  and  to  the  point. 
The  book  has  no  padding  about  it  and  deserves  an  immense  sale." 

SAMUEL  POTTER.  M.  D., 
President,  Milwarikee  Academy  of  Medicine, 
Aathor  of  Index  of  Comparative  Therapeutics,  etc.  etc. 
1&ff~  Sent  free  on  receipt  of  price,  $  1  .OO. 

DUNCAN  BROS., 

131  &  133  S.  Clark  St.  CHICAGO. 


THE 
FEEDING  AND  MANAGEMENT 

OF 

INFANTS  AND  CHILDREN, 

AND  THE 

HOME  TREATMENT  OF  THEIR  DISEASES. 

By  T.  C.  DUNCAN,  M.  D., 

PRESIDENT  OF  THE  AMERICAN  REDOLOGICAL  SOCIETY.  CONSULTING  PHYS- 
ICIAN TO  THE  CHICAGO  FOUNDLINGS'  HOME.    CLINICAL  LECTURER 
ON  DISEASES  OF  CHILDREN.    AUTHOR  OF  "A  PROFESSIONAL 
TREATISE  ON  THE  DISEASES  OF  CHILDREN"  (2  large 
volumes).    EDITOR  OF  THE  UNITED  STATES 
MEDICAL  INVESTIGATOR,  'ETC.,  ETC. 

MRS.  J.  E.  JOICE  writes  :  "I  find  it  a  very  useful  book  and  full  of  practical 
information,  especially  about  diet  for  children." 

L.  PAULY  M.  D.  writes  :  "I  am  glad  to  know  that  we  are  going  to  have  a 
German  edition  of  The  Feeding  and  Management  of  Infants  and  Children. 
I  know  of  no  such  book  in  German  of  a  similar  character  and  am  confident 
that  it  will  be  welcomed  by  all  thinking  German  mothers." 

MRS.  T.  WILCE,  President  of  the  Mother's  Society  of  Chicago,  says  :  "It 
is  the  most  instructive  book  for  mothers  and  c  specially  young  mothers, 
that  has  come  to  my  notice  and  I  earnestly  arlvise  all  prospective  mothers 
to  read  it.  Would  to  God  that  I  had  had  such  a  book  years  ago. 

MRS.  H.  E.REDEKER  of  Kenosha,  Wis.,  writes:  "I  think  it  isthe  best  work 
of  the  kind  I  have  seen.  1  am  glad  that  I  shall  have  Dr.  Duncan  at  hand 
ready  to  consult  at  any  moment  for  I  have  the  greatest  confidence  in  all 
that  he  says.  It  is  a  book  that  it  seems  to  me  every  mother  would  like  to 
have." 

DR.  EDWARD  CRANCH,  Secy,  of  the  American  Paedological  Society  (com- 
posed of  the  leading  physicians  interested  in  Children's  Diseases),  says  : 
"  I  have  carefully  examined  the  work  and  unhesitatingly  pronounce  it  a 
most  necessary  book  for  all  families.  It  ought  to  go  into  every  intelligent 
household  where  the  health  of  the  little  ones  is  valued." 

'•Prevention  is  better  than  cure,"  and  many  a  babe  will  fare  better  if  the 
mother  follows  the  advice  given  by  that  great  friend  of  our bebies,  T.  C. 
Duncan.  It  is  a  work,  whose  first  par  c  we  can  fully  endorse,  and  since  I 
studied  th^se  alkaline  and  acid  babies,  my  endeavors  are  to  have  my  little 
patients  alkaline.  The  artificial  feeding  of  children  is  a  most  interesting 
study  even  to  an  old  physician  and  only  by  following  closely  the  rules  laid 
down,  can  we  prevent  the  necessity  of  studying  the  secoud  part.  —  North 
American  Journal  of  Homwpaihy. 

The  Organon  of  London,  Eng.,  says:  "Paedology  is  Dr.  Duncan's  Specia- 
lite  and  we  may  be  sure  that  what  he  writes  on  tnis  subject  contains  some- 
thing worth  reading.  His  Encyclopedia  on  Diseases  of  Infants  and  Child- 
ren is  a  work  for  the  profession  ;  this  one  is  for  the  public,  and  a  better 
work  on  the  subject  we  do  not  remember  to  have  seen.  *  *  Every  day 
rules  for  diet  and  regimen  generally,  are  what  the  public  should  know,  and 
without  these  the  skill  of  the  physician  is  daily  thwarted  ;  iu  this  respect 
Dr.  Duncan  has  performed  his  work  almitably.  The  book  is  elegantly 
gotten  up." 

SOLD  ONLY  BY  SUBSCRIPTION. 

Price,  Cloth,  $2.00 ;  Half  Morocco,  $2.75, 

Agents  wanted  in  every  town.  Ladies  sell  it  rapidly.  Address  for  terms 
and  territory, 

DUNCAN  BROTHERS, 

131  <&  133  Clark  St.,  CHICAGO. 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 

AN  INITIAL  FINE  OF  25  CENTS 

WILL  BE  ASSESSED  FOR  FAILURE  TO  RETURN 
THIS  BOOK  ON  THE  DATE  DUE.  THE  PENALTY 
WILL  INCREASE  TO  SO  CENTS  ON  THE  FOURTH 
DAY  AND  TO  $1.OO  ON  THE  SEVENTH  DAY 
OVERDUE. 


OCT  17  1934 

OCT  15  1937 

LD  21-100m-7,'33 

